Garmin GPS-Where to buy for best price

Unless Garmin has changed things, you do not need the RV760. My Nuvi760LMT has four modes. In both RV and truck modes I can configure height, length so it will direct me around not so good roads. You might try searching for that model as well as it has been out for three or four years now, so discounts might be more available.

I've been looking for a discount dealer for the RV 760LMT too. I really like the fact that you can configure your rig's height, weight and length, and it will use them to avoid low clearances, etc.

I price all over but usually end up at the "thegpsstore.com"

I've been very happy with "gpscity.com".

The only Garmin made for RVs is the RV-760, I am aware of no place that discounts them ( I checked last week, well, because).
There are some others that have "RV" mods, but they don't include built in things like campgrounds (which is easy to add via POI)
Personally I like GPS-City and Tiger-GPS for service and prices.