The Patriot Thunder comes with the C13. Good engine, it has served me well. Lots of power, towing a Suburban I get about 7.5 miles per gallon driving in the Rockies.
You will probably need new rubber unless it has been replaced.
New it was probably about $350k new (that was the sticker that was on mine), so the price is not unreasonable. I paid $150k for mine in 2009, but it has some issues I knew about.
Support from Monaco is no worse than for any of their other coaches, they have all the technical information on your coach.
Drive it, inspect it, try everything, and if you like it, buy it.
2006 Patriot Thunder