A couple things...
First, wearing contacts underwater (in a dive mask) is not a good idea - lots of things can happen (contacts can slide around or get lost completely), and even if all goes well, it's a very compromised experience.
Not sure if you know, but dive/snorkel masks can be bought with prescription lenses. Yes, it costs some money - exactly how much depends on your prescription and the kind of mask you choose. If you (or anyone who requires corrective lenses to see clearly) want to see stuff underwater, a prescription mask is the way to go. I'm an avid scuba diver, and have been using a prescription dive mask for years, as has my wife.
If your prescription is a common/simple one, you can buy a mask with "pop in" lenses (using standard prescriptions) surprisingly cheaply. If, on the other hand, your prescription is not a common one, then you would need a custom mask. They can (and do) make them in any prescription. I currently use a bi-focal mask - the lower part corrects for near vision, so I can clearly see my watch, dive gauges, camera viewfinder, etc., and the top part of my mask corrects for distance, so I can see the sharks coming :).
You do not need to be a "strong swimmer" to go snorkeling - far from it. The standard way to snorkel is to lay on the surface, face down (so you need a mask and snorkel...), relaxed, essentially floating. You float because people are naturally buoyant - as long as you're breathing! You wear fins on your feet which make it super-easy to propel yourself. Snorkeling is easy - or should be, once you have the right gear and someone shows you how to do it.
Before you resort to "underwater scooters" and other gizmos that will compromise your experience (and will be very expensive), do yourself a favor: find a place where someone can show you how to snorkel properly, how the gear works, and how easy it actually is. Then, consider investing in a good dive mask with prescription lenses, and an hour of "pool time" with an instructor who can get it all sorted out for you - for less than the cost of a couple trips around a beach on Uncle Bobs Crazy Underwater Vespa.
Where to go: Find a local scuba diving shop - one that teaches scuba classes (almost all of them do) with access to an indoor pool! What city do you live in? Any decent sized city or large town will have one or more scuba shops, with a pool, where they give introductory lessons. Go talk to them and be honest: tell them about your vision challenges (bring your eyeglass prescription with you), they will be able to tell you if can get an easy pop-in mask, or if you need a custom one that costs more. Explain you are not looking for scuba classes, but want to try snorkeling when you go to Hawaii - but you need to learn about your options for a mask, and get instruction on how to do it.
You really owe it to yourself to at least investigate this. Any kind of made-for-tourist underwater ride gizmo (I've seen them) can not compare to actually having the freedom to "swim with the fishes". Trust me, this is something you can do. Once you learn how (and have the right mask) it will change your life.
Good luck.
