>>1474690The minimum you need is a bike of
- cassette rear hub
- threadless headset
- slick tyres ( invest in those, $50 in tyres is worth $500 everywhere else )
- good fit
You can get it for $500 if you shop around. Here in EU a basic Decathlon road bike ( Triban RC100, pic related ) will push you back $300 and is pretty good. Drop $100 in tyres and helmet and you are good to go.