One thing about having a adjustable frame is that look how "coolers" have changed in 25 years, with the old bent pipe frames you could never start running the Yeti or Rtic coolers, their dimensions are way off what igloo and other outfits produced. I bought my frame sticks from a metal outfit in Spokane Valley, they were a lot cheaper than what NRS was charging for the same metal. Rafting is so great because you can tweak your boat to exactly what you want, I've tweaked my frame 3-4 times now and I'm still learning. I'm trying to come up with a gun rack(chukars) that protects the gun yet is a fast grab. There is nothing better than a fall hunt down on the Salmon river.Finding the anodized stuff similar to NRS and some other outfitters is hard...but just finding 1.25" Schedule 40 aluminum pipe should be a lot easier (and cheaper). There is a Aluminum specialst outside of Denver called Alreco that has a ton of selection and weird stuff and even they don't carry that stuff.They can order it...but you basically have to order more then any hobbyist would be able to use in a lifetime. Some raft frame manufacturers like DRE will sell you a stick or two, but its like $6-8 a foot rather then $3 a foot. Easy enough to just spray paint it or even better get it powder coated and if you shop around should be able to do it for cheaper then buying the anodized tube. NRS does sell bare tubing kits with 2-4 pieces for fairly reasonable prices too... that is what I did for my 146DD frame with the Whitewater Machineworks Double Barrel Fittings.
If you get it from NRS or similar that is true... but there are plenty of places that specialize in rafting stuff that will make it custom to your dimensions and preferances. Custom work is more spendy though... so getting something "off the shelf" will save you money in exchange for it possibliy not fit your needs directly. I will also say that there are places like Recretec, Jordan River Boatworks, Riverboat Works and Downriver that sell "off the shelf" standardized frames (as well as custom work) that have been doing it forever and know what works for most people and sell it as a standard package.
If this is your first multi-day setup... you may not actually know what your preferences are, so starting with a more standardized frame package that has some adjustability might be the way to go until you figure out what you like and don't like.
Its certainly possible to make your own stuff based on your buddies stuff or just looking at specs from the raft fabricators and your boat specs. Speedrail or Lo-Pro fittings are your friend since they only required a drill and something to cut the pipe to length to put together. You'll need to buy a few things like oar towers that are hard to replicate in the home shop without welding and machinist equipment.