DRV 43 footers - Dallas and others - Actual purchase prices?

I would bet the dealer paid wholesale for this trailer. So you need to find out what wholesale price is on the trailer, if you want any bargaining power.
There are several pay websites (30 dollars or so- penny wise, pound foolish applies here) that will look up the wholesale price for you.
Than tell the dealer you know the wholesale value and will only pay X amount above that. Most likely, they will agree to that amount. They are no different than a car dealer.