Howdy
Once you have determined the model fifth wheel you want, just Google the model and you will find lots of info on pricing. You may also notice msrp prices vary be dealer for the exact same make/model. This is because msrp is a dealer set number (unlike the auto industry). The best thing to do is find the lowest out the door price online and use that as your offer.
As far as trucks, my SRW 1 ton truck in signature handles my 12k fiver well and have 500 lbs payload to spare. I would recommend a DRW for any fiver that exceeds 14k gvwr.
Good luck