This PDI might be the dealers own inspection before you do your own personal inspection before taking delivery.
Our dealer did a very thorough PDI of our trailer before we ever showed up to take delivery. They had it in one of their bays for a couple of days. I don't know if they found any significant problems or not but there wasn't any saw dust to be found any where... so I know they at least looked and cleaned every where.
When we arrived to take delivery we spent about 3 hours with a tech going over all the typical PDI punch list items on our own.
We were not charged a PDI "fee" but I'm sure the dealer had his cost built into the out the door price we paid.
If a dealer truly believes they need to charge $1300 to insure the RV is completely functional without any defects before the customer takes delivery... you have wonder about the quality of the units they receive from the manufacturers.
On edit:
I forgot to add... I wouldn't pay it. The dealer should already have any prep time figured into his costs of business.