That’s one thing I like about RC. It’s large enough so that a normal healthy lifestyle can be obtained, yet not large like a New York or Indianapolis type city that is crime ridden and almost beyond hope of salvaging. Plus it’s close to the mountains and provide a great scenery to enjoy. Right now, though, it’s hard to find a realtor in RC that deals in rentals. I’ve made inquiries only to receive no responses.
The one down-side to RC I don't like is Sturgis Rally. The entire state is over-run with Harleys. If I lived there, I'd take a two-week vacation to somewhere else.
Zillow shows a bunch of rentals in the RC area. See: Rapid City, SD Rental Properties. The number of properties and availability depends on what type of place you're looking for. Naturally, a single-family home is going to have a higher rent than an apartment/condo or townhome.
Another site to consider is NeighborhoodScout.com. It has several maps that show things like real estate prices, crime areas, etc. See: Rapid City, SD.