I think time is the big factor in build offs to be honest so you have to pick a reasonably popular one, a low rider one would be good but then geographically speaking the US is really the only country for supply at a cheap price and there is very limited places outside of the US that supply parts and at a relatively cheap price, at a guess if I were to order from around the world (Australia is closest to NZ that sell genuine underground lowrider parts but still not cheap and limited range too) your looking at around maybe $2,500/$3,000 to do a quality but basic fresh new build, maybe a pre 1960 British bike build off would be fun, plenty of those all around the world, and with a guide line that it must be original era frame and fork with original decals I.E not repainted and no repop decals but unlimited to what parts to put on, plenty of brands back then raleigh, rudge, hurcules, philips, BSA, rover, royce, royal enfield, southern cycles and so on, you get the drift there have been well over 200 bike companies in England over many years