To the OP, you might want to up your budge to $350.

I've found that (like guitars) folding bikes usually have a higher list price than what they actually sell for. There are sales, older models, floor models, etc. There's also Craigslist, where you can bargain or find good deals.

I just had nice ride with a lady a week ago. She was riding a Dahon P8 and enjoying it immensely. She bought it from Craigslist for half of the list price.

In my case, I paid $550 for my complete Swift. It was the last "old" model from Gaerland (It was 18 months old; -$50) and a floor model (-$50). They fully tuned it, and I used the savings towards some Big Apples.

To me, the best folder under $300 is a misnomer, because you can get more than you bargained for. You should include mid-line Dahons and especially Downtubes (if you can find them used).