"I only saw one used P300 Power Plant for sale (not sure if that could be loaned out) or the current Power Plants at new retail price."
You have to call them. Demos are not listed as inventory. Also, they will almost certainly lend you the used P300. But you don't have to stop there. They'll send you other power products as well. When I bought my line conditioner, they sent me demos of PS Audio, ESP, Furutech, Shunyata and Jena all in one box.
Its really important to demo power products. Its not like IC's and speaker cables, where you can make some general assumptions as to how they will sound. I could try a power cord or conditioner in my system and love it, but put the same thing in your system and hate it.