Yeah, I think LA trains allow you to bring bikes on at any time--without restriction to size and folding.

I no longer live in LA but it's my adopted hometown and I know the areas listed in this thread well. I grew up just a smidge outside of DTLA. I was checking LA Craigslist for awhile and still do occassionally because I was considering keeping a folder at my mom's for when I visit.

I would agree with Mtroup, you will get better value from a used full size bike. If you're determined to go with a folder, just beware of the compromises that come with a folding bike.