The cheaper PST kit is the bushings and Ball joints and only the outer tie rod ends.
If you compare the PST kit with bushings, ball joints, idler arm, both inner and outer tie rods, ($379) then its only $20 less than the PPM Extreme duty front end kit, and for the #399 PPM price you also get the center link and with the PPM kit you getting Heavy duty service parts.
I just got my PPM Extreme kit last Thursday and installed the Bushings and Ball joints over the weekend. I've never done anything with the steering and suspension on the front end of a car before, but so far so good. I rented a ball joint press from AutoZone. I highly recommend renting one of these, because not only does it press the old ball joints out and the new ones in, one of the cups that comes with the press fits the size of the control arm bushings so it worked great to press the old rubber out and the new Poly in. The only part of the install that gave me trouble was trying to keep the new lower ball joints going in straight. The lower control arm has a slight slant to the top surface were the cup on the ball joint press sits. This causes the press to be at a slight angle and it was a pain to get the ball joints started straight.
Anyone that has PPM kit, if your pressing in the new outer shells, go ahead and sand off the powder coating on the outside of the new shells. The first one I tried, the coating scraped off as the shell went in anyway and it made it harder to press in. I sanded the powder coat off the other three and they went in easier. Don't sand the inside of the new bushing shells, they have a machined surface to help hold the grease around the Poly. That is another bonus of the PPM kit that the PST kit does not have. I paid extra to get the Roadmaster Centerlink and I guess those are not in stock yet because I did not receive it last Thursday with the other box.