I spent about 400 bucks on heather's semi dry suit, but I bought a henderson gold core 7mm suit for her. It is lined with a hydrophobic satiny soft material, and it fits very snugly to prevent water from getting in. It is actually so dry that she has to add water to it at the surface, because otherwise she has a hard time sinking...it holds a lot of air(good because its not cold water!)
Fins, booties, snorkel, mask, hood, gloves, some mask cleaner, and a set of cajones will take you a long way as a casual diver... we went out and bought wet suits for our first dive vacation (i picked up a 3mm jump suit and was fine in costa rica, which has cool pacific water). That was the first year I bought gear in 6 years of diving.
I'll probably buy another Gold Core for myself once I recover from the cost of the first one... we like the Cressi Big Eye's masks and since I left mine in costa rica in about 100 feet of water with a current, i'll probably buy another... We will be buying regs, and bcd's before we take our rescue diver course in may. Probably a pair of suunto Vyper computers (nitrox compatible dive computer) because we just did the enriched air course. After that it is steel tanks and dry suits

You can totally go nuts gear wise, but like dave said, good gear lasts a long time.
It seems like diving in this area is fairly costly per item. They want you to rent the whole shebang. It would cost significantly more to pay the "per item" rental price for each item to make up one dive setup than it costs to rent a full dive rig, if that makes sense. They get your money either way. So we figure if we are doing a lot of diving, its a lot better to have our own gear, and have nice stuff we love.
I really like having a dive computer, especially for multi level dives. The Recreational Dive planner alone leaves you with a lot of air in your tanks. It is amazing how much more down time you can get with a good dive computer, beacuse it is doing the math real time, as opposed to rounding.
Nitrox is your friend.
That's all i have for now.