Well, not quite. There is no evidence of an agreement to payment terms for the dirt
Doesn't matter, in fact if they were paying to get the dirt then it'd be less likely to have been a criminal act under the law, it's that they were going to be given the information for free as per the email that created the criminality.
only an agreement to meet to talk about it.
And this is Conspiracy against the US in terms of violating the Election Laws, penalty is up to 3 years in jail.
So it's really two issues that are not at all clear: 1)Is merely meeting to talk about getting dirt a crime?
Yes, because it's an action that is made to further the Conspiracy agreed to in the E-Mails.
2)Is there not-currently-public evidence that some kind of quid pro quo was agreed to?
It doesn't matter, no quid pro quo is required.
Here's the thing, the offer in the email to give dirt on Clinton that had been gathered by the Russian Government was illegal. The correct response is... "No thanks, er can't have anything to do with this." followed by an Email to the FEC to tell them that you have been approached illegally.
Accepting the offer to meet becomes a Conspiracy to act, and taking any action to further that Conspiracy, i.e. setting up a meeting, cements the Conspiracy as a Criminal action.
Had Jr taken this email to the Manafort, Kushner, and his dad, and they had said, nope, we can't do that, and he'd then emailed back, "Hey ignore my previous email, we can't act on this," again, we wouldn't be here arguing about it, but they didn't. They went ahead with the meeting, and in doing so committed the offence of Conspiracy against the US.
Look at it this way. I come up to you in a pub and offer you the chance of a life time to rob a bank. If you say no, you haven't committed a crime. If you say "sounds good," then you are potentially committing a crime. If you then come back before any other steps have been taken and say "I changed my mind, I'm out," then again you haven't broken the law. But, if you say, let's have a meeting to sort out the details, and then set up the meeting and bring in the rest of the crew expecting to be setting up a bank robbery, then yes, you have committed a crime, even if the end result of the meeting doesn't have the outcome of creating a bank robbery plan and the bank was never actually robbed.