I can buy a 70's road bike for under $100 here in Oz, and only that much if I want a decent one. You can then convert it to SS for nothing ... as I did to my daughter's bike, or you can buy a cheap freewheel for $20 and maybe lash out on a chain for the same. Fixed gear with brakes will cost you a fixed cog and, if you're feeling like throwing money around, a chain.

There is NO reason to buy a Walmart bike... well, not one you'd admit to your mother in law.