With luck and patience it's doable.

Luck in finding a good bike to work with. 80's road bike. Double cranks, everything (brakes, bottom bracket, front wheel, headset, all in good condition and the seatpost not fused into the frame.

You want a conversion, not a restoration.

Patience in waiting for such a find to come along for less than $100.

If everything about the bike is good, then the only matter is removing un-needed drivetrain components and getting a rear wheel.