My personal opinion is that the Rio is too far and isolated. The Rio is with three casinos (Palms and Gold Spike? I always forget the name of the small one) and the shuttle only runs until 12:45am/1:00am. It's a massive property, but my opinion is that if you are looking to save money and do not want to stay on the strip, why not stay on Fremont Street? It's a great atmosphere and you'll be able to easily cab to / from the strip if that's your desire. Plus it's within walking distance of the outdoor outlet mall if that is your thing.
If you want to stay on the strip, the Best Western @ Casino Royale still does not charge a resort fee (as far as I know). And the big plus is you are right on the strip in the middle of a lot of different casinos (with varying price ranges to suit everyone's budget). TI also has a no resort fee type rate (I think it's called the "TV Offer") but I think the catch is that it's Sunday to Thursday or something like that.
Either way, I would much rather stay at Fremont or the Best Western/TI than stay at the Rio. Unless you have been to Vegas a lot and want to keep trying new hotels, it seems silly to stay in such an isolated location.
(and that's just my opinion, so no offense to Rio fans)