Hi Jester,
Good to know you'll be visiting this august.
Check out the ff sites, they'll give you some info on Subic.
http://www.divephil.com/subic
http://www.master-dive.com/
I went diving there 3 weeks ago, we went to ScubaShack, they charge about USD28 for 2 dives w/equip then you give the DM a tip. It was raining really hard that day and the water was dark brown at the surface but it cleared up below 25ft, the viz was not crystal clear but it was good enough to see the wrecks. It's mostly wreck diving in subic btw. We dove the LST, nothing much there except for the really big grouper that stays there. The other dive is the El capitan, a bigger wreck, longer penetration. They say the best wreck is the USS New York but we weren't able to dive it because the viz was bad. Another thing, if you plan to dive in Subic, it's best to stay there the night before because the best viz is in the morning and generally gets bad later on. You can get a room at the boardwalk which is just in front of ScubaShack, the rate is about USD30/night. There are other hotels inside the base with various price ranges or you can stay just outside the base in olongapo. The trip from Mla takes about 3hrs each way if you have a car, longer if you take the bus.
If you have another day to spare, you can do a day-trip in Anilao, about 3hrs also from mla. There are a lot of dive resorts there where you can choose from. We usually go to AquaReef or Outrigger-ScubaWorld. The day trip includes 2 dives plus lunch, they also rent out gears. From there, you can decide if you want to dive around anilao or take a longer boat trip to Puerto Galera.
PM me for more info. I have a mla-based DM-buddy who's accredited in those shops, he also organizes small dive groups that you can join, he can also help you in your transpo, they usually depart mla early in the morning and return to mla in the evening. perhaps he can help arrange your dives.
Good Diving!