For a first build, there's something to be said for the box store bikes, my first was a $200 Chinese Schwinn, with pretty much what you had in mind Motorbike - a long term test drive
I was getting an unknown/untested (to me) super cheap engine so I wasn't holding my breath much heh - building the motorized bicycle taught me a bunch in a hurry about both motorizing a bicycle and what maintenance & repairs would be needed in a worst case scenario, using a cheapo bike taught be a ton
about bicycles with little investment.
Thing is I expected it to be a POS, it didn't frustrate me when stuff broke & I knew
it was somewhat hazardous with the potential for frame breakage and the inevitability of rim failure - I jut wanted to tinker w/stuff and see if it was worth my time. I couldn't in clear conscience sell the thing & wouldn't ya know it... the one time I let a buddy ride it is when the front wheel tacoed >.<
BUT overall it turned out to be so much fun & once the China was worked out, reliable enough I decided I'd take the lessons learned and build a better one - which in the long term turned out to be about the same cash investment interestingly enough. I think where the problem is lays in people's expectations - you can
build a motorized bicycle for about $250, but yer gonna pay for it in attention, if ya know that and are willing to pay the price then it'll be a blast. If you expect anything
other than a somewhat labor intensive, hazardous & disposable toy - it'll be little more than disappointment.
Building a motorized bike is easy, building a economical, reliable & safe one... now therein lays the challenge lol