There has been a lot of discussion about bicycle quality here; cheap-o verses the more expensive bikes. Here's my experience so far.
I've had two Schwinn Jaguars, Chinese built and sold at Target, that have served me well both accruing well over 1000 miles. Never had an issue with frame integrity, bearings, brakes etc. The Jag normally sold for about $150. That's considered a relatively inexpensive bicycle.
On both bikes I disassembled and checked wheel, crank and steering bearings and relubed although they had been properly lubricated from the factory.
The welds, paint and finish on them were high quality. For general purpose riding I couldn't expect anything more from a bike.
Now, let's look at a $700.00 bike built by a big name U.S company. They have a good reputation for manufacturing quality bikes. Even with the high dollar name I still took a look at bearings and was disappointed to find them all nearly dry. The crank bearings especially looked as if someone ran a greasy finger over them before assembly.
The kickstand mount is welded to the frame and the frame is bending where the stand attaches. That happened before the engine was installed so I can't blame the extra weight. The factory paint would chip off down to bare metal with the slightest impact. The shifter cable housing is cracked and falling off of the spiraled inner sheath and the bike has only been out of the garage a few times.
To be honest I'm not optomistic as to how well the frame will hold up to being motorized and I truely do not expect to put as many miles on this bike as the cheaper Schwinns without the possibility of some frame repairs down the road.
How much you spend isn't always a good indicator of bike quality. There are those here that will poo-poo on the Wally World, Target, K-Mart bikes and wouldn't touch anything made after 1960 or if it says 'Made in China' on it. There is something to be said for early bikes; like everything today, quality isn't the main issue to manufacturers anymore yet quality can still be found and it isn't always at the high end of the dollar scale.
A little research on what bikes are popular and have been successfully motorized will help the decision making process a little easier when it comes to choosing the right bike for you.
Tom