Steve: I see no responses, so I will offer a little guidance from our experieince with our Class A.
The carpeting cost will depend greatly on the quality of the kind you choose. Since there is not a lot of yardage, an upgrade in quality does not break the bank. The install cost will be the shocker. There is a lot of custom work in lots and lots of small sections, and the experienced/good installers know that. They price their services accordingly.
From what I recall, the install cost was 150% of the cost of the actual carpet (and we went with a pretty durable carpet).
New carpet made a BIG difference in the cleanliness and homeyness of our rig. We are really glad we personalized it in this way.
Good luck with your project,
Ken & Deb (WIT Club, FMCA, SKP, Harvest Hosts, and grateful volunteers with SOWERs)
2005 Winnebago Vectra 40FD w/400ISL and Allison 3000MH on Freightliner's Evolution chassis, Onan QD7500, 1000w Renogy solar, BlueOx tow gear, and 2015 Cherokee TrailHawk toad.