Your best bets in my opinion are RaceDayQuads.com or GetFPV.com (if in the US at least). For having someone custom build you will likely need to pay quite a bit more than something that is "off the shelf" with some predetermined set of components and configuration. Quads that are off the shelf or out of the box get made in the 100s-1000s so quantity of parts ordered at that scale things can be relatively economical (economy of scale). CiottiFPV on YouTube has recently started to offer to build quads likely with some customization, but not likely he would want to take on something completely different from what he's offering either (he or any company would then have no way to make guarantees about the quality of the thing since little to no experience with it).
I know that's why I'm leaning twords a radio and quad that doesn't rely on a off shelf that relys on an app from my phone to fly. I live out in the middle of nowhere with miles of swampy, wooded nothing. All I'd really want is a return to home failsafe. But a radio and bird that aren't reliant or connected to anything but themselves. I had a Hubsan 501s but the range and flight time was nothing where I am. So after flying strait up 100 ft or so and locking in my home point I'm good enough at it to just cruise around. That's all I'm after anyway. I just want to be able to get out there a little and enjoy the wildlife. I'd be in around $700 I guess. Like to get some good solid wattage and antenna set-up. Super low kv, running slow with as many lions as would be appropriate.
Appreciate the obvious neglect by those who are experienced to enlighten me as to at least a crumb of information as to the basics of where to start based from my objective.... Like a Radio??? Take care all, I've got this lol
Your plan sounds fine to me get a radio with swappable transmitter module that runs openTX like radiomaster T16 compare the various T16 and T18 transmitters available would be my suggestion. For receiver I trust the spectrum satellite ones a bit more than frsky just seem to work better in my limited experience but so long as have TX with 4 in 1 module and swappable can always change out the actual radio part of the transmitter/controller. Also good to get some experience in some of the simulators using the transmitter you choose most any with usb connection and openTX will work with some fiddling sometimes on most computers.
Regarding off the shelf ones for long range there is a newish hexacopter all the youtubers I watch reviewed will see if I can find one here think it will fit the bill:
It is totally fine to buy any betaflight compatible quad (really FC just needs compatibility) and then hook up a receiver to it and bind your transmitter to the receiver then configure the receiver input using betaflight configurator.