3 weeks to build an exiting 30lbs machine. It is possible, given tools and basic materials.

Batterydrills are the basic you need.
Most feathers use batterydrill based drives. From the whole batterydrill tieripped to a piece of MDF to the gearboxes remade in CNC'd works of art (Ranglebox and REC spring to mind, and it seems Gimson is back on track too).

If that local place sells motors with build on planetary gearbox, it depends on the power (less than 100W is asking for failure) end speed of the outgoing shaft ( 700rpm is good. Less than 10mm diameter is asking for trouble), and the suitability to get a wheel on them.

Weapon. Forget a decent spinner. Too dangerous without a good arena.
Maybe an axe, cool and always pleases the crowd. Cheap electric scooter or step motor and chain drive, and you have a start. (search for My1010 chinese electric motor)

ESC's can be a matter. Brushed motor esc's are getting rare in the RC world, and if you find an affordable one, it most of the time doesn't have reverse.

I hope this is a start for you.