Spare wheel for the turbo...

Hi folks - I've just set up my indoor torture facility in the garage, and after the first ride I've already noticed a change in my rear tire. I know that wear is accelerated on a trainer, and plan to get a trainer tire this week. However - I need a spare wheel to put it on. It clearly doesn't need to be an amazing one, and I'd like to keep the cost of it down as much as possible. It'll need an Ultegra standard 10 speed cassette on it.

Any suggestions? Thanks in advance!