Your friend has talent. What are they worth? I haven't a clue. But I think he should hone his works down into something that's a little more coherent, and he could really have something.
That kind of work is great for people who like to stare at things for hours on end and find all the neat little things hidden in there, but it appears to me like he's trying hard not to make any kind of a statement of his own. And it seems to me that it's hardly art unless you're really expressing yourself.
So, as it stands, I might give him $50 each, maybe $75 depending on the frame and my mood.

But if he'll concentrate his energies on something with a little more focus, I think he could make a good living for himself.
Just MHO, and I'm no art critic.