PPL IS one of the largest consignment lots in the U.S. They have been around for a long time and also do a large in-person and mail order RV parts business
As you would expect, they have a complete range of priced units and units in a complete range of conditions. It is indeed a good place for you to start looking, as it is not too far from where you live and you can see a wide variety of coach brands, ages and sizes all in one place. They also do a pretty good job of updating their website: http://www.pplmotorhomes.com/
It is hard to make HP recommendations, as it is really HP/gross weight that really matters. Most (including me) feel 1 HP/10 pounds of gross weight (coach plus toad) is adequate. So for my 22,000 pound coach with 2,500 pound toad my Cat 250 HP is more than adequate. If this were a coach and toad grossing 37,000 pounds, a 350 HP would not do as well.
And you will be able to find some nice gas AND some nice DP's in the $70k price range. Certainly with older coaches, how they were maintained is critical. On diesels, do not be very concerned about miles. I would rather see a 12 year old DP with 140,000 miles on it than 14,000. The drivetrains were just not meant to sit idle for months at a time.