I full-timed it for awhile last fall
and winter in a Casita
(about 5 months), and my expenses were way lower than that. Of course, I boondocked, so take away all the RV space rent. But if you're out West, where I am, you can stay way cheaper by boondocking
or staying in BLM and State park campgrounds.
I spent a lot less on gas, also, by staying in one place for a week or longer. I even camped in an exclusive rural subdivision for several days waiting for the high winds to stop so I could move on - they hadn't sold one lot and I had the entire place to myself, gorgeous views. I went up into B.C. Canada and did the same (one of the side benefits of the housing crash). Nobody seemed to notice or care.
Groceries weren't any more than at home, maybe less, as I tended to eat out less (i.e., none). My propane
expense was low (even in the cold, it was 15 below several nights in W. CO) and I had no electricity.
I think I lived on less than $800/month - just me and four dogs. That included $100 for cell and wireless internet (air card). And we did fine, we ate well. I just never bought anything extra, like souvenirs or books (no room anyway).
Just pointing out that you can live WAY cheap if you boondock. I'm in W. Colorado/E. Utah, so it's easy here, but I was also in Idaho, Montana, and Canada, and it's the same.