The Shopsmith bandsaw shouldn't be run faster than 1000 rpm, which gives it a blade speed of just under 2900 fpm (feet/minute), which is plenty fast for wood. As I understand it, aluminum should be cut at around 1000 fpm (350 rpm), and steel way down at 100 fpm (35 rpm). If all I wanted to do was cut wood, then a standard 1750 rpm motor and a two-to-one pulley setup would work just fine. But I wanted the option of changing speeds, and getting down into the 300 rpm range was going to require big pulleys, and/or an idler setup. (For a bandsaw with 11" wheels, fpm = rpm × 3.14 × 11 / 12, or, fpm = rpm × 2.88)
Happily, it turns out that good quality variable speed motors can be had for free. People give away treadmills all the time -- usually after they realize they need help to get them out of the house. About a week after I started thinking about the bandsaw, someone in my neighborhood put a working treadmill out on the curb, so I grabbed it.
In addition to the motor, I saved the heavy duty casters and their axle bolts. I also pulled some electronic components off the console board to add to my spare parts collection.
Tip: Bring a friend. Treadmills weigh between 150 and 200lbs. And they're big: mine just fit in the back of our Subaru Forester."
Tip #2: If you can, get a treadmill which uses a slider control to control the speed. Newer models now have "speed up"/"speed down" buttons, and the motor controller may not be as simple to use. (The slider on older models is just a volume control (potentiometer), and you can just replace theirs with one of your own.)