I invest in the Black Hills, Northern Hills and Rapid City in addition to elsewhere in SD. I've operated STR in the Black Hills for almost a decade now. I was one of the first to AirBnB and I was operating it remotely. At one point, we accounted for a significant percentage of AirBnB revenue in South Dakota (not necessarily because we were good, but because we were first :)
Here is what I believe. The thing about Sturgis is that it's a one time a year booking. I've had multiple short term rentals available for Sturgis for nearly a decade and I have never been 100 percent full. You're right though that rates increase for Sturgis. For revenue planning, you should use a 75% vacancy rate for the Sturgis window. For your $150(ish) duplex, I'd say you can bump your price to $275 to $315 per night and get booked, if the unit is 3 bed 2 bath, probably marginally more.
If you are looking for a PM, Dena Sheets is the person you want to call for Sturgis/Northern Hills. She specializes in Rally Rentals.
I disagree with Jaron Walling. It isn't a good idea to remotely manage a side hustle cleaner. WHEN they fail a job, you have to refund a guest and they are left with the task of finding new accommodations or having their stay at your place sullied because of a terrible first impression. I can get you some cleaning company leads if you PM me.
The last thing I'll say about Sturgis, and I'm going to get roasted for this...But it's an unspoken secret around here (because we don't want it to be true), that Sturgis is dying...The rally goers are aging out of the ability to ride their motorcycles anymore and they are getting bored with it.
I have more I can share, but this is getting long and if you have specific questions, you can send me a private message.