You can get a matching spare from your local tire Company, such as Les Schwab, just buy the same size tire as you have on your car and buy a Spare tire Rim which they should have and it shouldn't cost you more then $120. or if you want a spare tire doughnut, you will have to go through a dealer.
if your talking about the spare donut one, you can get one very cheap at a junk yard. maybe even free. look in your yellow pages and call around first though.