Its not like we know nothing about the galaxy. In fact, we know many things, such as the size, the star distance, size, metalicity, planets, etc.
We have a good idea of the general picture, yes. We aren't perfect on details, and there's still that nasty Dark Matter/Dark Energy thing that we have to figure out, but yeah, more or less, we have a decent idea.
Yet there's a lot of things we still don't know yet, especially including the fine details. "Life" would be one of those fine details.
Just because our ocean is 100% explored,
lol wut
You're wrong again. You might want to look into that.
why do we need to spend millions of dollars to look for "little green men"?
Ah yes, "little green men", the thing someone says when they want to mock others, and just look silly their own selves...
Talking about the possibility of life, and the active search for life, are two different issues.
Why do we NEED to spend millions of dollars to look for alien life? We don't, really. We don't NEED to. Nor do we NEED to study fruit flies. We also don't NEED to understand the theory of evolution. Sure, it's useful, and probably good for our long-term survival, but in the sense you're speaking of, we don't NEED to do anything at all.
Personally, though, I'm with Carl Sagan on this issue, and I find his ideas far more compelling than your own.