I wish I could buy 3rd party RAM for a MacBook Pro unless they finally stopped soldering on the RAM recently, then I would love to buy a new MBP with my own cash if I can get a normal keyboard.
You would probably only save up to $200 on third party memory. Which is not nothing but if you get a 15 inch you’re already talking about $2400
On the other hand, the price delta between Apple prices for the 16GB -> 32GB upgrade is about $250 more for the 15 inch than you could get from a third party if that were an option but you’re already spending at least $2400 on a 15 inch MacBook Pro.
Don’t get me wrong, I’m arguing hypothetically. I’m not spending my own money for an expensive laptop. I don’t need portability for my personal computer. I need portability for my work computer and a job will give you a work computer - and hopefully one that is beefy enough to do what you need.
My personal development computer will always be a desktop. You get more bang for your buck and I hate developing on just a laptop without external peripherals anyway. I’ve never been interested in Apple laptops enough to spend my own money over just getting a much cheaper mid range Dell when I needed the portability.