Motor to spin slowly, low torque
If you drive the wheel with a belt driven by a 2mm toy motor shaft turning at 5000 RPM you would need the pulley to be 100mm in diameter. 

That sounds feasible. If you need the pulley to be bigger, put a small pulley on the motor. Easy to make if you have a small lathe, should be easy to make by sandwiching bits etc. if you don't. 



If you're not in too much of a hurry you can get DC gear motors for &lt;&lt; $10 from China like the below 12VDC 10RPM model with a convenient 6mm shaft. 



This, like most gear motors, will have relatively high stall torque- it is 5.6 kg-cm rated.. if you need it to stall without damage you may need to limit the current.