Acting on a tip from Mark Evanier's website, I went to my local Barnes & Noble earlier today and found several copies in the discount book area, marked down to under $25. Since I've been seriously tempted more than once at the full $150 price I grabbed a set and ran. A very fun book! Just something to look for if you get a chance; they had a few at that price on the B&N website but they're sold out there now. Check your local store, though.
Now if I could just find the Far Side collection that cheap...