I kind of agree with clhjsh that Motorhome Tires may "match" (or come close) to the package price they quoted if it can be proven that you can have the same product and services done elsewhere for a lower price. But do some research so you can back up the prices you are asking them to match.
Remember, there are other online options available other than through Amazon at the same price. Some vendors will provide you with a list of installers near your location. Some will even provide installation prices for those installations services so you can compare (Carid and SimpleTire come to mind, for instance but I believe other online tire vendors provide similar services).
Someone I talked to the other day said that using some other online vendors other than Amazon, gave him better personal service as he could call them and ask questions such as date codes, etc. I'm not sure if Amazon will give such mico-service or not.
Just doing a quick search, here are some other online vendors offering the 245/75R22.5 L for around that $314.72 price with free shipping.
CARiD
tires-easy
BBWheels
bestwheelsonline
SimpleTire
Obviously, it would be better to have them dropped shipped directly to the installer's location if having them installed off-site. Check and make arrangements with installer ahead of time it that's the case.
You also can have some places come to your location if you wish to have them installed in your driveway but you'd have to call and see what installers would charge for such a service and compare it with the quote you received from Motorhome Tires that had it incorporated into their pricing package to see if it's worth it to you. Who knows? You could still beat that price if you pieced it together on your own if the convenience of having it done without moving the rig is important to you and, again, you could at least attempt to have Motorhome Tires match the quotes you researched.
So let's say it's about (and I'm just guessing as I haven't priced commercial tire mounting recently) $300 - $500 range to have the tires mounted and installed and $400 --again, just guessing-- to have an installer come to you, you'd still beat the price that Motorhome Tires initially quoted you.
(
Here's a price list for tire services at TA but I'm not sure how up-to-date it might be and what other charges might be incurred for the installation total ...they've listed $42.99 per tire to mount but I'm sure there will be added charges to that for miscellaneous stuff)