Some factors to consider
1.) What will you do with the footage? If more personal you can do fine wiith even some of the entry level Sony's (have not went through all the reviews on the HC5/7 yet, some buzz indicates the now discontinued HC3 was about the same) and you probably get get better quality than that. The Canon HV20 has gotten very good reviews (but no Gates Housings)
2.) What features are you looking for? In general one of the more important things to access is White Balance, which Gates now has in the housings for even the low end Sony's, though of course the more items you can access, such as shutter speed and other items will help with more shots. (With your number of dives my guess is mutlitasking/buoyancy will be easy for you.)
3.) What type of diving do you do? Good conditions? Bad conditions (viz & light)? Both? If you do more real clear nice light diving you can get good results.
Using B&H Photo as a guide for prices (some places have things listed for less and many are legit, but beware the real cheap places) and ballparking pricing
Camera - $1160
Housing with mod for WB (projected) $2400
Plus one or more ports
Fathom WA Port $895
Gates WA Port $595
Gates Basic Port $115
So for $3600 or so (using basic port) you are in the HC7
The next level is the FX7 type camera - larger camera and more weight (the HC7 rig altogether about 8 lbs, FX7 20 lbs or so)
Camera is $2600
Housing $3995
Basic Port $450
So about $7000
Of course this is an overview and there are more selections/choices but wanted to point out some issues to start with to think about to help narrow things.
As an aside, I like Gates alot and the Fathom ports are VERY good. I like mechnical housings and Gates are built like tanks. I think the first thing is to figure out (a) is the $7000 range plus your range and (b) does size/portability come into play. I am subject to travel restrictions so that is always a big factor for me.
HTH get you started. (And the Sony's play nicely with Macs)
EDIT TO ADD: You can also find some deals on non-HDV 3 CCD cam set ups sometimes for less and that also something to consider, again depends on the budget, the PC series of the Gates were nice