That link does have good pricing, but be sure to calculate with shipping and factor in the tire cost. That stuff is heavy and shipping can be pretty doggone high.
You can use L/T tires and save a little money on the conversion, then get true M/H tires 5 years down the road. Converting your wheels will also help future resale.
I would contact a local tire shop as well. If you show them the internet pricing, they might be able to work something out for you. The shop can also look up your specs. and ensure you get the right offset and tire size. I prefer to keep that kind of purchase local to support businesses I will need in the future, plus you can just drive up and have them inspect the tires before you head out on any trip.
All that being said, I was able to work out a deal with a local tire shop for $185 a tire for 16.5" Firestones (6 total). We don't know that we will keep this RV more than 5 years, so that was a better value than changing out the wheels. Something to consider.
Jose
