We had one when DynoJet came out with them. Back in '98-99.
We charged an hourly rate. Just to set up and take off the dyno is a production in itself. So factor that in. Also, like mentioned, we were a repair shop that offered lots and lots of clutching and gearing options.
The important thing is to figure out how to use the dyno so it shows on the mountain. This means several hundred runs on your personal sleds to figure out how much brake to use, ambient temps, backshift runs etc.
Usually the minimum people ended up spending on the dyno was around 4-500 bucks. That's 3hrs on the dyno and whatever clutch parts we ended up using. Usually around 100 runs. 3 runs at a time to be thorough and do it properly.
Very unlike a car/truck dyno where you strap in, make a half dozen runs, and pull her off to brag to your buddies. You will be lucky to do a proper job on two sleds a day. and usually two people working the process the whole time. It can be done as a single person, but there's a lot of running around and set-up that just makes it easier when there's two.
Good luck, have fun, when done properly it gives a great baseline to work with. We guaranteed 15% HP increase from first run to last run. Complete with backshift test to prove that we weren't just loading up the weights and running a super stiff spring. Without a backshift test you can deceive yourself, and many others. The sled may make huge power, but fall flat on it's face on the hill. That's why a backshift test is important. Keeps things sane and numbers realistic for real world riding.