Interesting thread and a worthy goal. I tried to go through my costed bill of materials for my build to get the price down to $1K and I had to delete everything that would make it road legal in Michigan. No headlight, taillight, brake lights, etc. Things like lights, batteries, chargers, and all that really rack up a tab! Basically it's a bike, motor and good brakes. The Phantom Bikes Gray Ghost and the Ridley 1903 are both around $2500 and neither are road legal.
$2000 and two cases (one Left Hand Brewing Milk Stout and one Lion Stout) and I would be comfortable knowing I was putting a friend on the road with a reliable ride. Build first, beer later....
In the "spirit" of the thread:
Felt Cruiser (any Al frame) can be found at local shops, eBay or CL for about $350 - $450 average about $400 (I paid less so I know it's possible)
Ridley Model 48 Kit $650 http://www.ridleymotorcycle.com/motorbike/engine_48.htm
Sturmey Archer Drum Brake eBay $80 http://www.ebay.com/itm/Sturmey-Arch...item43b07d1760
Bike shop wheel rebuild labor $40
Over budget but then the Ridley is over priced. Maybe they'll work with you on that but: $1170, call it $1200ish. Lots of room for those in the know of with real skills to save money. Not road legal. Beer won't be cheap either!