Base price for the 2012 Cougar High Country 321RES is 40,628, The 2013 base price is not listed at NADA.com but should be somewhat close to the 2012 price.
I can't give you any indication of problems with the model, however I am sure others who have experience with it will offer their thoughts.
You will find that no matter which travel trailer you choose, you're going to pay an "arm and a leg" for fuel. Whether you drive a diesel or a gas truck is not the issue. Fuel expenses are pretty much the biggest expense in travelling after the RV cost is eliminated.
As for your price quote of $35,000, it is about $5500 less than the base price and seems like a fair deal depending on what "add on" charges the dealer puts below that figure to increase the bottom line.
Good luck on your decision whether you decide to buy this or another RV. Just consider the expenses of towing are just a part of the "joy of RVing" LOL
2015 F250 6.7l 4x4
2014 Cougar X Lite 27RKS