I'm hardly an expert on packs but here's my recommendations that perhaps some of the more active users can confirm or put down:
Check out
Members Only Swap Meet . Odds are you'll find a good deal on a used pack in decent condition. A lot of the guys on there are like tech-gadget geeks that have to have the latest and greatest and get rid of their current gear to fund the news stuff. Or their missions requirements change and they sell what they don't need. So the used items are generally in very nice condition.
I just opened this thread to ask Lightfighter if there is any way to attach a belt to a R.A.I.D. pack. I don't have any personal experience with this pack so I don't know.
R.A.I.D. question(s) If there is a way to attach a belt, this might be a decent pack to look into, mainly because of the various customization options with the PALS webbing. It'll cost a little more in the long run to add various types of pouches and pockets to it, but the upside is that you can break it down depending on what you're going to be using it for.
Another option may be the Eagle Ind. MOLLE STYLE A-III-P (A-III-P-MS) or any one of the other 3 Day Assault packs with external webbing.
It's really hard to recommend one particular pack to someone as some people wear differently than others. I would say any of the 3 Day Assault packs would probably get you where you want to go. The ones with the PALS webbing will obviously offer a little more in terms of expansion.
I'm always a little skeptical when people start talking about doing any kind of entry/CQB while wearing a pack. It reduces your maneuverability in tight spaces and puts you at risk for getting hung up on something stupid like a door knob or coat hook or knocking somethign over. Unless you train this way and your training environment takes every possible thig into consideration when setting up. But its difficult to compensate for that extra "volume" on your back... think of it like driving a car with a big trailer on it for the first time and trying to parallel park.
For doing CQB I'd say just stick with wearing a tac-vest/harness and a low profile bladder system. I don't do this for a living though, so get a second opinion but the people I've worked with only went in with what they needed. There is no need to have all your crap on you for CQB when it's obviously a temporary mission where you're not going to be for an extended period of time.