If you can find STPP locally by all means go for it, the Chemistry Store while somewhat decent in price, does charge a handling fee on top of UPS delivery. It might pay for one person to order a 10lb bucket and divy it up.
Maytagmom and Venus, if you all want to try some of the phosphate laden Ecolab detergent from my stash, shoot me an email and will send you a sample.
Finding Fels can be hard, but check your local supermarket's laundry section, however sometimes they put it in with the bar soaps. Also check fleaBay for both the vintage and newer versions.
Personally prefer the old "Purex" version of Fels soap for both having real "Naptha" and that it contains washing soda, whiteners and lots of other "detergent" ingredients. Since my stash of vintage Fels numbers about 40 or so bars, think am set for the duration. *LOL*
L.