When I first put my bike together....it was roughly 1000 bucks including the bike.
It's friction drive- you could get a decent bike, a thatsdax motor and friction drive and be well under a grand. I like the friction drive because it's so simple. Sure, it has some disadvantages-the chief one is that you can't ride when it's wet out.
Try changing a flat tire on a wally world bike with a frame mounted engine......I can change a flat on my bike in less then 5 minutes. I guess that comes from my mountain biking days- back then I could change out a tube and be back riding in less then 90 seconds :-)