Some of us thought the bathtub drone project looked like fun so we're researching the idea. Testing indicates that nobody's lawnmower is going to fly with a passenger but it seems that treadmills use motors up to 3 hp, 6 of which look like they would do the trick. The big holdup right now is propellers. Seems you can get small ones at the hobby shop at pretty reasonable prices, probably because they get crashed and broken often enough that mass production drops the prices. When your payload gets to 220 lbs however, the required prop tends to be the sort that real aircraft use and those don't come cheap. The other problem is that if I were building an electric ultralight, one prop would suffice and one that size wouldn't be too bad. On a drone where you need 4 to 6 props, the size falls between large hobby and small aircraft and is much harder to come by.
Preliminary testing suggests that 1-1/4 hp/motor would lift a large drone if the pilot were limited to a lightweight dummy and the actual pilot were operating it from the ground. This opens up the path for building the structure and sorting out the control software first, then upgrading to more powerful motors later.
As has been noted before: Engineers should never be unemployed.