If you can afford it and like to just build... stay in DIY.. If you want a bike you can build once and more or less ride it a while inexpensively, the China Kit bike is a pretty good deal. The bike and motor should be doable for about 2hundred. Using a new kit on your existing bike or a cheap thrift store bike you recondition.
The bike I am building now came in at under one initially, but the motor was on a drastic sell out and I paid twenty for the bike at a thrift shop. I had parts all over the shop. so I could mix and match as well. To but to be honest I build, just to build.
This is supposed to be my last build, so I am doing things I would never do, If it were just a cost effective build.
When you do DIY you can never anticipate all the things you are going to have to buy. It's completely different pot of fish stew. For one thing you are making it up as you go and you are going to make mistakes. For instance two days ago I was smoothing off a bad weld and ruined the frame, which I had been working on a week. I just tossed it and moved on to a different frame. You have to able and willing to do things like that, when you are working without a playbook. So even though we talk about DYI builds and how cheap it was, that isn't really true in my case it's usually really how cheap it would be for you to duplicate what I built, because hopefull you won't be making the same mistakes I did
Right now I am converting a big, big huffy 26" cruiser to a 24" with the harbor freight motor. I am building that last bike, I hope. Or I would just stick with the 20" wheels and ride it till I had another great idea. which aren't that great. It came with 26" and I'm just not that tall, when you add ten more inches for the motor, I would need a step ladder. It is ready except for the thirty five dollar 24" coaster wheel on the way from Amazon. When it gets here today it will be ready to go.
The wheel will get finished thanks to a lot of ideas from you guys. Duct tape for liner strip to cover the spokes ect.
Another example of things you don't expect was the harbor freight engine. It had a gas tank that had to me the worst piece of crap I ever saw, set on top of a great engine. I ended up spending the last two days making a weed whacker gas tank work on it. That is the type things that happens when you build DYI.
So in summation the man ahead of me was right... Most things are difficult and tend to get more expensive as you go along. The first bike I built was a china kit and I'm glad I did it. I sold it because I didn't like all the maintenance and ended up building bikes that are disposable in my opinion. To be honest if you want a bike that is cheap to build, Cheap to run, and only need to go five miles to work, then come home five miles, build and ebike from a scooter. If you want to ride it all day, you are going to have to go gasoline. This last bike with the HF engine has been the most dependable to ride off and on all day, just for fun..
I have stripped the motor from my ebike to make this last build, but I have all the parts and batteries to put it back together on a moments notice, and probably will just to have one.
So why do I personally do it. I like to challenge myself in a build. Sure I build the simplest of all drives, and they will tell you the least efficient and I will say to them... so what? I figured last night i get about 50mpg, if I'm running it just to play around. I might could squeeze 10 more if i was careful not to let the drive slip on the wheel. Maybe even 10 more if I lived in flat country. So if I counted the miles like the scooter company guys do, I would claim 75 mpg. But 50mpg in my area is more honest I think.
Sorry I hi jacked your thread but if you have the ambition and resources build DIY with any weird bike/engine combo you can imagine. If you need safe, stay with a kit. That's my opinion/