I was just in Maui last week, I and did most of my diving out of Lahaina as I was staying in the northern part of Maui (Ka’Anapali). Not sure if you’ve been to Maui before, but what I really liked about it was the ease of shore diving. As far as the area you are staying in (Kihei), I was told of a really good shore dive in the southern part of Maui called La Perouse Bay. Although I didn’t dive the area myself (was just a bit far for me to dive), I was told by numerous locals it was a great dive due to it’s isolated location and its proximity to a marine preserve just to the south of La Perouse Bay. I was told you can pretty much park right along side the road and you’ll be along a black rock/pebble beach (apparently only divers go here because there are better beaches north to lay out on) and the water entry it right off the road, not more than 20 ft from your vehicle. I wrote a blog about diving in Hawaii so check it out if you’d like. I wrote about another great/easy shore dive in the town of Lahaina (site is Mala Pier). I’m not sure about any dive shops close to Kihei (I’m sure that they’re there) but I used Lahaina Diving while I was there, it cost 7 bucks to rent a tank and 5 bucks to rent weights (I owned and brought all my other gear so I’m not sure if you’d be in the same boat as me as far as only have to rent tanks/weights). I do know that another shop (also in Lahaina) Dive Maui, also rents tanks and weights (5 bucks for each, so you’d save 2 dollars a dive) I’d use one of those shops if you choose to dive the Mala Pier since they could tell you about the site in greater detail as its a site used by all operators in the area as a back-up boat dive (when the conditions are rough else where). Have fun in Hawaii, if you end up diving La Perouse Bay, let me know how it was. Also, if you have the opportunity to dive Lanai, take it...it was my favorite dive location during my visit.
Mike