Yamaha make great bang-for-the buck acoustics. You might be able find a used Ovation in that price range, too.
Hmmm... not big on Ovation.
The rounded plastic back is bloody annoying and keep slipping off your lap. and the ones I've tried - MIK and American - are just missing that warm vibe that you get with most acoustics in the same price range. But admittedly, they play bloody great and have beautiful soft v necks.
I find that acoustic guitars are much more inconsistent than electrics in terms of tone, you really just need to shop around and find a sound that you like, and a lot of people find it in very cheap guitars but not in the more expensive ones.
And keep in mind that the timbers in a used acoustic will have 'mellowed' a bit more than a new one.