Check out this consignment facility just to give you an idea for your price range and what year you would be looking at. It also gives you floorplan ideas. There are quite a lot both gas and diesel (look under that section, too) available within your price range.
The one thing with a motorhome is sleeping arrangements. Your children are getting tall and a dinette bed is short. Sleeping two boys on a RV sofa could be cramped plus you mentioned 'when grandma visits'. Making up a sofa bed and storing linens could be a hassle.
Travel trailers can be had with two bedrooms or bunks.
I hope you find what you want as the boys would love it, I'm sure.
As someone stated, if you want the 'camping experience' have you considered renting a cabin/park model in a RV park? Many state parks have yurts, too. That might be a cheaper way to go for short trips. Sometimes they have a campfire ring, too! :)
PPL Consignments
