While I'll agree PWP is terrible usually, bear in mind you can also pay with points & cash, online at americanexpress.com/travel or via 800-no.
Lately I found myself in nearly the exact situation mia describes...on an airline I fly infrequently and have no status or stockpiled points, and which isn't a MR partner. (USAir...traveling to GCM)
I used points for half the ticket, cash for the other. At least that way I wasn't emptying out my MR and also wasn't paying my left kidney to go on vacation.
It was a great trip AND I got to be there while my best friend got scuba certified. Was actually glad to have had the option.