On average, you can expect to pay around $1,000 to $1,500 per week for a medium-sized RV motorhome in Montana during the month of September. However, prices can range from as low as $700 to over $2,000 per week depending on the factors mentioned above.
To get a more accurate estimate, it's best to contact several rental companies and compare their rates and availability for the specific dates and RV type you're interested in. Be sure to ask about any additional fees or charges, such as insurance, mileage, cleaning, or pet fees, as these can add to the total cost of your rental.
Additionally, keep in mind that September is a popular time to visit Montana, so it's a good idea to book your RV rental well in advance, especially if you have specific travel dates or preferences.