Can I ask why you are looking to replace all ten air springs on a 12 year old coach? Are they all leaking or are you having issues? Air springs generally last much longer than 10-12 years. I just changed mine about a year ago but that was on a 19 year old coach and I could have easily gotten at least another year or two out of them other than one was struck by some road debris.
As for cost, $750/each is crazy. I paid around $165/each for mine and a common price was in the $165-$185 range.
If you can find the part number there are many sources for OTR trucks in which to purchase them from.
Here is a common Monaco S-Series air spring. This Contitech AS8897 replaces the Firestone W01-358-8897 that is listed in many Monaco Owner's Manuals.
https://www.truckandtrailer.parts/Co...91_p_1509.html