Go to NADA's web site and look up your 2010 Sunseeker model 3100. Plug in the mileage of the unit you are looking at, see what values are shown, then plug in the additional mileage that you expect to put on it in a year. Don't worry about plugging in options since you are only looking for the difference due to mileage. That will tell you the depreciation to expect due to the mileage. Of course, you have to consider that you are buying retail from a dealer and may not be able to resell for retail.
I have noticed that NADA allows up to 15,000 miles the first year on a new motorhome without additional depreciation, but only 5,000 miles per year after the first year.
I'm curious about the "Banks Power System". Which Banks components are installed? Power chip, air filter, headers, exhaust?
As for the price, look at a new one. Bob Ledford's Adventure Motorhomes in Greer, SC, has new 2013 model 3100's (without full body paint) with a price on the window of under $60,000. If they are too far from you, check another Forest River dealer.
RV Motorhome dealer | New & Used RV Sales & Service |Greer, SC |Adventure Motorhomes
As another point, be sure the three of you can fit the sleeping spaces. We have a 2011 Sunseeker 3100. The dinette and couch make into beds, but they are both short for me and I'm only 5'10" tall. If one of your group is short, you will be fine. If all of you are 6' or more, well, you'll have to work it out.
Good luck with your golfing. Keep the forum posted about your purchase decision.