Thanks to my mom, and the fact that she sometimes reads my blog, my dilemma regarding a mask for use in Hawai'i has been solved.
She pointed me towards Snorkel Bob's to rent the prescription mask. You can get a mask, fins, snorkel, and bag for right around $45 for rent for an entire week. That's significantly less money than just the mask was going to cost me to buy, so I'll definitely be going that route.
She says that they are like Walgreen's with how common they are on the islands, so you can rent them from one shop and return them to another if need be.
So, needless to say, that will be one of the first things we do is get those rented, that way we can have them for pretty much the entire time we're there.
Good call on Snorkel Bob's, mom!!