Personally I like Www.ebikekit.com. Ask for Jason (he answers all the emails). Tell him Mike Fairbanks referred you (not that I get anything, but maybe he'll give me a discount on my next kit).

Anyway, ordering a kit from him is so easy. It's a hub motor. If it's for your wife I'd recommend a front wheel hub motor (much easier to install).

You can install it on your own. If not, a bike shop can easily do it too (but will probably cost you 50-100 extra bucks).

It's really not difficult at all. The first time you do it you might think it's frustrating, but once finished you'll think, "hey, that wasn't so bad."

Then, after a while you'll be able to install, uninstall, and reinstall over and over.

If I had a front wheel ebike kit delivered I could have it finished in an hour, easily, and so could any of the other folks who ever built one.

And they really do work (and work well). They are fun and safe (if you don't overpower them).

The biggest challenge is battery technology. The best batteries generally cost as much or more than the entire kit.

You can get a kit for about $300 and a good battery for 300-500 dollars (for a lithium-based battery that's light).