While there are always exceptions, I'm guessing most startups that are around the 10k user mark have plenty of free low hanging fruit left in terms of improving a user's experience or getting more traffic in general. Whatever you end up doing, you're going to get a lot more bang for your buck with a more optimized flow.

Personally (and without knowing more about what you guys are doing), I'd spend the $2k exploring different avenues to get a better idea of what kinds of things do and do not work. It's hard to know what may or may not work sometimes without trying it, at least a little bit. Seemingly similar startups may have very different levels of success with things like untargeted Google Adwords, targeted Google adwords, other methods of product placement, etc., and while you can't always get conclusive evidence from $2k, it's a start.