The Gospel of Mark is the first story of Jesus that was written, and all others are dependent on it
Price gives a reasonable outline of the pedigrees of the gospels.
Mark's the earliest, a common-speech narrative from an urban gentile church, somewhat prior to the destruction of the Second Temple, about the time of Paul's latest letters, thirty years or so after the (purported) time of the crucifixion.
Luke and Matthew both rewrite Mark, Luke for a gentile congregation and Matthew for a Jewish congregation in Galilee, adding more material from a book of the sayings of Jesus they both had access to, and other sources they didn't share. Their versions of Mark weren't the same, btw.
John (who might be earlier than Matthew) is certainly writing for an urban gentile congregation with some heavy gnostic tendencies. It's impossible to tell whether he had access to any of the other gospels, or was working with his community's collection of writings that overlapped with the synoptics' sources.
If he'd been Jewish, he would certainly have felt obliged to cite directly, but for a gnostic Christian there may not have been any similar compunction.
However, in the closing 3 paragraphs, Price goes off the rails:
The fact that all three of the other narrative Gospels in the Bible are based directly or indirectly on the Gospel of Mark demonstrates the lack of other narrative information about Jesus. The Gospel of Mark became the root of the other Gospels because it was the only writing that provided narrative details about Jesus. The additions that the authors of Matthew and Luke made to the Gospel of Mark are primarily just the virgin birth narratives and some additional post-resurrection narratives.
There is also language that is shared between the Gospels of Matthew and Luke which is not in the Gospel of Mark. The most well known proposed explanation for this is the "Q" document theory, which purposes that there was some other source document which both the authors of Matthew and Luke used, but was not used by the author of Mark. An equally valid explanation is that both Matthew and Luke are simply based on an expanded version of Mark, or that what we call the Gospel of Mark is a shortened version of the original, which the authors of Matthew and Luke used.
The Gospel of John adds a few additional narrative elements to the synoptic template, but the Gospel of John is a much later Gospel, probably written some 40 to 50 years after the Gospel of Mark. The additional elements in John are basically a gnostic theology element and a "miraculous signs" element, both of which appear to be inventions of the author himself. Some scholars propose that the "miraculous signs" narrative in the Gospel of John is derived from yet another source, but it actually seems to be a narrative element designed by the author as a polemic against the Jews. The "miraculous signs" narrative in John shows Jesus doing many "miraculous signs", but then at the end says that even after all of this the Jews still didn't believe that he was the Son of God. Thus, this narrative advances one of the agendas of the Gospel of John, which is portraying the Jews as unreasonable betrayers of Christ.
Let's take these one at a time....
The fact that all three of the other narrative Gospels in the Bible are based directly or indirectly on the Gospel of Mark demonstrates the lack of other narrative information about Jesus. The Gospel of Mark became the root of the other Gospels because it was the only writing that provided narrative details about Jesus. The additions that the authors of Matthew and Luke made to the Gospel of Mark are primarily just the virgin birth narratives and some additional post-resurrection narratives.
That's simply not the case.
Each gospel writer was trying to do the same thing -- for his church (which at that time meant a small group meeting in each other's homes) to collect the accepted stories about Jesus into a narrative, and by default leave the other stories out. They're writing the canon for their group.
And each gospel writer had to deal with all of the different stories that were circulating orally and in codeces (a codex was a kind of book or pamphlet, as opposed to a scroll) at the time and place that he wrote.
In fact, that was the whole reason for writing -- to sort out the mess. Keep in mind, we have literally thousands of Christian codeces from the first couple of centuries CE, and that's undoubtedly a tiny fraction of what was in circulation.
Mark was the earliest biographer we know of. And obviously, it was the first successful attempt to write a canonical biography of Jesus.
Matthew and Luke -- written after the fall of the Second Temple and the destruction of the Priesthood, probably a few years before the start of the 2nd century -- used Mark because it had become accepted by their groups (among others). It wasn't the only source, by any means, but it was a privileged source.
I'm also surprised by the glib way that Price tosses out phrases like "some additional post-resurrection narratives". Here, he's talking about the apostolic witness, which sets up the whole dividing line between the true-apostolic (Jamesean) groups and the Pauline/gentile groups, as well as the ascention, which places Jesus firmly in the company of the highest of the annointed men of God, such as Elijah.
What seems to have happened here is that Price understood the basic source scholarship, but then made incorrect assumptions about the paucity/plethora of sources to draw his conclusion.
Then there's this:
There is also language that is shared between the Gospels of Matthew and Luke which is not in the Gospel of Mark. The most well known proposed explanation for this is the "Q" document theory, which purposes that there was some other source document which both the authors of Matthew and Luke used, but was not used by the author of Mark. An equally valid explanation is that both Matthew and Luke are simply based on an expanded version of Mark, or that what we call the Gospel of Mark is a shortened version of the original, which the authors of Matthew and Luke used.
Let's be perfectly clear about one thing. This "equally valid explanation" is
made up out of thin air.
Nobody has ever run across any "expanded" Mark or any reference to, or even hint of, any such thing.
"Expanded Mark" is a pure invention of the imagination.
What's worse, Mark is a relatively crude, and certainly early, document. It has been added to. But no reason is known -- or, to my knowledge, has ever been proposed -- why anyone would want to cut material from Mark.
The claim of equal validity here is simply false.
As for his comments on John, it's definitely gentile, and it certainly asserts the miracles, but it then consistently makes the point that seeing the signs isn't the important thing, it's faith in Jesus (and having your whole household join you, if possible).
There's really nothing remarkable there.