You need a contactor from a central air conditioner compressor unit. The pull-in coil on these is 24 volts, which is the same voltage as many yard sprinkler solenoid controls. If you have underground sprinklers and have an extra circuit, just set that circuit for when you want the compressor on. This way you could program the compressor to be all pumped up and ready to go when you set foot in the shop.
If you looked around a little bit, you might be able to find a contactor that ran on 110 volts, and then you could use the bathroom fan timer. Some of our center pivot irrigation machines use 110 volt pull in coils, but they are for 3 phase, but would work in your case (you just would't use one set of terminals).
Hope this helps: Tony would have some ideas, also.
