I've not actually stayed at Grizzly myself, but have been through the area several times, the last time exactly 3 years ago today when I fished the Madison. Yellowstone Holiday up on Hebgen Lake is pretty nice, but not local to the West Entrance particularly. Shunning the crowds, we inevitably stay further away such as way Northwest up the Madison River, or Southwest around Henry's Lake or Island Park. I'm sure you'd be quite pleased with Grizzly.
None of these popular, close-in parks are inexpensive of course
http://www.grizzlyrv.com/rates/ , but then you are well-placed for easy daily forays into Yellowstone, Hebgen or Quake Lakes, plenty of restaurants/fast food handy coming home after a daytrip, the museum, and souvenir and specialty shops (in my case probably the highest concentration of flyshops in the country
-Nervana).
I can say that even in fall, West Yellowstone is a busy place; so if you plan on Grizzly next summer, or any other park within 50 miles, I'd make reservations quite a ways in advance, if not now. In fact, I recall checking out one park (Lionshead?) while driving through one evening not that long before seasonal closure, and there were no openings.
-Joel