Depens what you mean by 'best'?
For $100 dollars you can get some decent TLRs as well as folders. A good TLR should beat most folders for optical quality, but they don't fit in the pocket too well. Having said that, a really good folder with rangefinder and decent lens would be way over $100, as would a semi-pro TLR, so you would need to compromise. A nice folder with rangefinder and budget lens could give you a very useable camera, but you might like to spend the same money on a very simple camera such as a Bessa or basic Ikonta but with a really good optic. Ditto TLRs, some of the Yashikas came with budget triplet lenses and are very useable, but go for the decent glass and you'll bust your budget. Not sure if any SLRs come under $100? Would probably be a beat up and battered if they did, which might mean they aren't a 'best' buy. Also,I've picked up cameras at junk sales for the equivalent of $10 which I've seen dealers selling for $100 because they've been cleaned and serviced - another requirement to factor in to the price.
Can you narrow your requirements down a bit?