Won't the RV shop give you an estimate? Without looking at it, it may be hard to give an estimate. It may be something simple like the cable unscrewed from the blade. Figure an hour.
If requires removing the valve and your tank has waste in it. It is going to cost you.
2021 Chevy Silverado LTZ 3500 Diesel
2022 Montana Legacy 3931FB
Pull-Rite Super Glide 4500