Powerfisher,
I looked back at your original post and sure enough - no suggestion of inexpensive (Sorry !).
So, 243 would be a good cartridge at 500 + yards.
http://www.gunnersden.com/index.htm.243winchester.html
But if you don't care about the pelts consider a 7MM or if you feel confident with your 30-06 - work up a hot load and go get'em.
Let us know what you end up with and good luck !