Another couple of things you may not have considered:
Are you sure you'll be able to get parts kits? I believe AUP only sells to AUP dealers (Aeris, Oceanic, Hollis). On that note, PiranhaDiveMfg sells a set of regs called Synchro regs. They even have a sealed option called Synchro "Ice" that are very cheap and have cheap parts kits. Not sure on the reliability, though, and you definitely don't have the "Name recognition" that gives so many divers the warm&fuzzy feelings. Higher quality regs than that would be Hog regs. They have a longer service interval and kits are available easily, but the kits are slightly more expensive than others. Getting the parts has been much harder than actually servicing my own regs. I was a Hollis-certified Reg Technician and had a HARD time finding parts. It took months to find them and minutes to service them.
One thing to consider is this: some manufacturers offer special deals to dive centers for their rental fleet. I know Oceanic was offering a HUGE discount on their Alpha9 regs if put into a rental fleet. I'm just not sure what the deal is with that in terms of requiring you to be dealers or not. It doesn't seem like you sell gear, so maybe partering up with a retail store on the island is an option? "We'll buy rental regs from you guys and send prospective customers your way, you sell them to us for cheap including servicing."