Sorry bub. That’s gonna take some research, enough I’d have to charge a consultation fee and you can’t afford me. But I’ll throw you a couple of free fish to help you along-
A monolithic upper is free float
You need to ask yourself seriously if you need quad rails, or the op-rod piston upper and whether or not either are worth the extra weight, complexity and cost
How many possible combinations of: uppers X barrels X stocks X piston systems…
There have to be 10,000s (if not more) of possible solutions. I was hoping some here had already built up such a AR and knew the weight and how much they had into it.
Honestly it doesn’t sound like you’ve done the proper reading unless you have some legit reasoning behind your build idea. Please share that.
I advise you research each part yourself so you learn what’s really best for you. We all have our own needs and ideas and they seldom include a piston.
Make sure not listen to TV shows that tell you a piston is such a big deal, too.
The closest things that you can get that are sounding like what you’re talking about would be a Colt APC, or an LWRC SPR of sorts since their rifles are self regulated gas with monolithic uppers on some rifles (if not now then soon) and then there’s the LMT MRP like justin_247 mentioned.
The LMT MRP is really close to this if you get the gas piston model. I personally own the 10.5" DI but for you I would take a look at the 12.5" gas piston. It does only have an “on/off” so if you really want to go full adjustable you would have to get a noveske barrel with switch-block and have it converted to the MRP configuration. Pricey but it would still fall in your budget. You might have to buy the upper and lower separately but LMT does make an ambi lower.
I think that it is something you could easily do yourself in that budget. If you don’t have the time, give the money to a trusted friend or associate and have them take the time to do it.
I would do it but I am not particularly well established around here so I don’t think that would help.
I am confused to whether you want an actual brand or someone just to CNC something for you custom (which I would not know the price point for). I do know that there was that legal issue where Mega was stopping production of monolithics due to LMT’s patent so LMT might be the only option here.
Otherwise, something like what TRIDENT runs, but with the LMT piston system instead of DI. Which is a LMT upper on a KAC SR-15 lower. But an AXTS AX556 would also work.