Re: First Bike build and limited to $600 ;3
With so, so many choices, I would google or any search engine with just those words. Also check local Craigslist, yard sales and my favorite, thrift stores. Some times you get really lucky!
With used or even brand new, from a store budget bikes. Be sure to give the bike an over haul. The most important safety feature of your build is the bike it self. No fenders (unless reenforced) and good front and rear brakes. A helmet that is more motorcycle then bicycle is a must have. MC rather then bike helps cars know your going faster then a bicycle.