Hi Kayla,
I have one rental in Rapid, a 2/1 SFH in the good part of town. I don't know the MFH market, but I do know that my property manager advised me not to raise the rent this year because the market is flooding with new apartment buildings being constructed.
One point you might be interested to know is that Keller Williams in Rapid used to be Kahler Prudential and they also had a property management division too which is still in operation, I'm pretty sure (I think it is Kahler Property Management or KPM). I chose not to go with them because they were rude to me. I use A&A and have been happy. NWE is another mgr in town, if they are still open, I haven't checked in a while, but I seem to remember they have more commercial and outlier residential. A new one that has popped up is Black Hills Property Management and I may be mistaken, but I think it is a one woman show and she is also a real estate agent for Keller Williams.
You might get an idea of what rent you could command by calling the Candlewood apartments, Kirkwood Meadow apartments (managed by KPM), or Harmony Heights these are west Rapid apartments that command nice rent, my guess is $850 - $900.
Ended up being a long post, and what I would tell you is that I exited the Rapid City market once the prices started to sky rocket in about 2012. Another reason I choose not to invest in Rapid anymore is because it got hit with yellow letters in about 2015 which means to me that there are too many out of staters who are now also competing. And the last reason, is that property taxes end up being a little higher in SD because we don't have an income tax here, so to make up for that revenue source, our State government takes property a little higher than other states.