Yeah discount tires mount and balance rates have gotten pretty ridiculous. Last time I went with the Z06 they wanted $125 to mount and balance 4 tires. You might try walmart instead. They usually charge $5 to mount/dismount and $5 to balance.
Or you can just buy a manual mounter, $150 one time and then never pay for mounting again! It's a bit of a workout, but you save a lot of money and time. Here is a great video that shows what is involved:
http://www.youtube.com/watch?v=Y3mPYtnl6Pg