If you didn't want to go quite that far, try pricing out an order of 20 or so packets on one of the mail-order sites with flat or low shipping rates for small items. Williams discounts dry yeast in quantities of 12 or higher, so it's $2.65/packet plus $6.50 shipping to my zone, anyway. So for 40 packets:
Personally, I find that focusing on improving my efficiency has given me an extra dollar or two in savings per batch, and I go through phases (make liquid-yeast starters, use dry, repitch, etc.). But it's your money!