Flip flop hubs are fine. It will cost about the same. If possible, get a fixed/fixed hub. You can run a single speed cog on a fixed thread, but you can't run a fixed cog on a single speed thread. Formula/nashbar/soma/iro/surly are all decent flip flop hubs that aren't too expensive. The suzue basics are also decent, but living in Boston, I would want a sealed hub. The only problem with french (peugot) bikes are that replacement bottom brackets can be expensive. YST just started making a threadless bb that will work for under $20, but I haven't heard how good/reliable they are yet.