[X4U] MacBook models to look for Used?

[catsoul]

I'm in the market for a used/pre-owned MacBook.  MacBook Pro would be nice, but my ceiling is $500, so…more likely to find a MacBook at that price or less.

What models of these machines are the ones to look for?  Am I right to want 2009 or later?

are 2007s simply too old from the standpoint of hardware, supported protocols, where OS X is now and where it will be?

Is the 2008 Mac Book the one to get?

Thanks for any thoughts on this.

Cat