Here is my original low-buck build, The Pig.
$128.00 kit (found a deal that week)
Free bike from the curb (I regularly scrounge on garbage day)
Free alloy rims and rear V-brake from parts bike
Homemade basket from a shopping cart
Bars and pedals from a wasted freestyle BMX donor
$10 pocketbike tuned pipe from the scooterstore junkpile
$25.00 BGF 36tooth sprocket (waste of cash since it was already worn out after only three weeks)
Automotive plug wire (free from pull a part while buying a starter. It fell in my toolbox accidentally)
$20.00 HD #40 roller chain (enough for two bikes per box)
Probably 20-30 hours labor building everything (free since I did it myself)
Total cash outlay: Less than $185 bucks
Sold it recently for $400 after riding it for two years problem free!