Mechanically inclined? I installed a Bafang BBS01 350 watt kit:
https://www.amazon.com/Bafang-BBS01-...ng+bbs01&psc=1
Put it on my old Schwinn CrossCut. I used a BiXPower 36 volt battery from Amazon (about $300).
Works great. Several hundred problem free miles. I like the mid-drive, as it drives through the bike's rear gears - I can downshift and unload the motor on the steeper hills. I went with Bafang's smallest motor and BIXPower's smallest 36 volt lithium battery for weight and size reasons - gives a nice "assist" to pedaling. I easily get 20+ miles between charges (using as an "assist" to my pedaling - I'm sure much less if used like a scooter...). I did have to use the Schwinn's combo brake/shift lever rather than Bafang's brake lever for the rear shifter, otherwise install was quite straightforward.
My wife has a BH Emotion hub drive. Also a 350 watt motor. Also a very nice bike. With hub drive, she has access to both her front and her rear gears when pedaling (the mid drive eliminates access to the front gears on mine) but her motor does not drive through the bike's gears. She can't downshift to reduce load on the motor on hills. At the time (about three years ago, I think) hers cost about three times what I paid to modify mine.
Suspect the alternatives are greater now - I see the Bafang BBS01 is still available- I would probably choose it again. Lithium Ion batteries are the way to go - recommend avoiding anything else.
Really pleased we made the change to e-bikes. Doing a lot more biking now - as I mentioned, using the electric as an "assist", so getting decent exercise and able to handle moderate hills and headwinds easily.