I can purchase the metal tubing locally here in Des Moines IA. to build a LWB for about $50.00. This is just standard mild steel ERW tubing. I usually find donor bikes in the range of $5.00 to $20.00 at second hand shops. I do all my own tig/mig welding so I can build a bike for about $200.00. If you can't weld then the price of having someone do it for you is pricey. Some welders charge up around $60.00/hr. Just to give you an idea on how long it takes to weld a bike, my LWB took about 80 hours. That isn't just arc time either, it is all metal prep and welding. A welder will charge time for metal prep unless you do all the prep yourself in which case you would tack weld and then have the welder do all the finish welding. So if you want to save money, learn to weld, it really is worth it in the long run. Besides, it gives you a new skill. Good luck!
Aaron W.