Sounds like you want to reuse the rim to build a new wheel which is generally not a good idea. Plus, you will probably need new spokes because the chances of the existing ones being the right size are very small, so no money save there. Plus, I personally wouldn't build any wheel, much less a fixed rear, with less than 32 spokes.

aebike.com has a Suzue 36 hole flip-flop for 25.99 and you can get an Alex rim for 15.99 - sure it's heavy, but it's triple box construction and it's cheap. Add some spokes and you should only be around $60.

http://aebike.com/site/page.cfm?PageID=30&SKU=HU4019

http://aebike.com/site/page.cfm?PageID=30&SKU=RM7509