Here's my take:
Find a good used quality bike with front suspension fork on craigslist, American if you like. Pay less than $100. Pick a reputable engine kit and install it. Upgrade to dual brakes, strong 12-gauge rear spokes.
This is your first build. Learn from it, work all the bugs out of it, then give it to your wife.
Then repeat the process for your better second build.
You should be able to build two bikes for $800.