Let me preface this by reminding everyone I have no experience in this area... The following is just using "business man" logic to point out details that would need to be looked into before the venture.
The first thing to address, the flight controllers that you can get individually. Are they not also going to have the same restrictions built in if they are also including GPS based flight? If they do as I would expect, then you would have to also be able to use an open source program that can do the same but would allow you to code it so it doesn't have those same restrictions in it. You may be able to work around those restrictions by locating a controller made before the laws were implemented ... maybe.
I would assume that most of the multi-copters with camera's are likely using integrating electronics for everything they can to keep the build costs down ( as well as keeping the weight down ) where they can. If you also narrow your search for ones that also have gimbal systems ( probably with built in stabilization as well )... they are almost certainly integrated systems that at most allow the use of different levels of cameras so they can vary their product lines. If we are also talking about a large company that is building enough to get a decent individual build cost discount ( ie build at scale ) and they are integrated as I am assuming, you end up with the same flight height restrictions still.
In the camera direction with a possible compromise direction that still allows a lot of options is the Insta360 GO 3S. It doesn't have gimbals but since it records 360° in one direction, you can edit the video to provide you whatever field of view you want in the end up to the 360° FOV. It also has built in stabilization. This coming in at a whopping 1.4 ounces ( 39 grams ). Just strap it on the front ( or where ever ) of the aircraft, hit record and go flying. Edit the resulting video after you get it back. Recharge the unit and go again if you wish. At around $270 they aren't cheap but neither are the gimbal camera's that I've seen that aren't even made for RC applications. Of course I don't believe this camera has any low light options, or ones I'd label as such. It also doesn't address the FPV portion at all either.
I can't see any RC camera options that will fit the listed requirements as going to be cheap any direction you take. In fact, of everything listed the camera and FPV options are probably going to be the ones that drive the costs up a lot. The next hurdle will of course be the altitude issue caused by laws in the USA.
