I just went through the same issue! Needed a bag for my SLR and camcorder while still having enough room for the kids' items. I ended up buying the Lowepro compudaypack. It has a separate compartment for a laptop, which we will be bringing on the plane, but not into the parks. Solved that problem. I like the personal items compartment because it's big. I can also use the laptop compartment for diapers, wipes, and changing pads for easy access.
The other one I was looking at from lowepro is the fastpack 200. It was about the same size on the whole, but the camera section was bigger than the compudaypack. This meant that the personal compartment was smaller. Not by much, though. The compudaypack felt better on my back as well.
I think I spent about $90 on it. Some of their other AW bags are double that. I don't know which ones (maybe all) were out of your price range, but I didn't think the fastpacks or the compudaypack were that bad considering the alternatives.