From what I've been told and seen, 'cost' is around 60% of MSRP - so something in the $60-65k or so would likely be a good, fair offer - they have to make some money or won't be around in the future.
Checking around (via web, phone, etc) you might find similar rigs listed elsewhere that would help you determine a fair offer for that particular model - some may be in more demand than others, etc.
Chris, Wills (16) Evie (13) & Toby our collie (6)
2011 Grey Wolf 28BH
2013 Chevy K1500 Crew w/ Reese StraitLine Dual Cam
Nights camped 2011: 11 2012: 18 2013: 12 2014: 12 2015: 13 2016: 56 2017: 8+