I'm not a real stamp collector, because I use the stamps; I do not buy the boring flags, but search out the pretties. If I'm going to mail something, why not use a stamp I like? I know I'm not alone in this - my friend A and I keep each other updated with fabulous stamp alerts.
It's one of the reasons I don't do all my bills online. . .maybe not strictly frugal, but definitely enjoyable to handle the stamps and envelopes and keep my nice mail carrier in letters.
A few years ago I discovered that USPS.com ships any size of order for just $1. That beats waiting in line at my little post office during their quirky business hours - only to discover a mediocre selection of flag stamps.