You cold look at Kelly Blue Book to see their "Buy it now" prices. To my knowledge, these are pretty close to wholesale prices. Remember, though, dealers can also purchase the autos from auctions which could mean the vehicles have been rental vehicles. There's probably no way in knowing the low prices that they've paid for the vehicles in this situation.
A bit off topic: I was looking at a vehicle yesterday that I was somewhat serious about. The dealer had a pre-printed CarFax report. I thought it was a bit odd that only one entry was present for the mileage area. I asked them to run another report. Sure enough, about 6 entries for mileage over the past two years showed up - and the report indicated the vehicle had once been a rental vehicle. If I had not asked for this second report due to my suspicions, I would have not known the full history of this vehicle. Also, it indicated that the dealer had picked the car up at an auction. I didn't mean to take this off-topic, but I learned a few good lessons that I thought I would share.
Back to being on-topic ...