This is a prime example why there not alot of stuff made for DSM's/VR4's. That l bracket is actually a square when it started life and has a good amount of waste.
So you want a set of brackets for 40 bucks. 7 to 10 of that is shipping then a 1/2 inch thick piece of aluminum is needed but not bar stock which is cheaper but a 1/2 in thick billet that's 12 x 12 inches for example. And 1/2 inch is probably to small 5/8 or 3/4 maybe needed. The brackets Ron had made by his buddy are exactly 1 inch so started life as probably 1.250. No one sells little pieces and if they do you paying the price. I just did an online search and 6061T6 is $58 for a 12 x 12 square .500 thick and $134 for 1.250 12 x 12.
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So you can get maybe 3 sets out of that. Just guessing. So lets say three sets now are sold. So far the builder is out 58 bucks and 40 in shipping to get you and 2 others there parts. Thats $98. So to sell you and your buddy and his buddy a set of brackets for 40 he's only made 22 dollars not counting his light bill to run the shop, mill time and or saws and not forgetting coolant for the mill and saw blades or any saw he's used to cut the pieces down smaller to fit in the vice, any finishing he does, bead blasting, paint or anodizing, end mills for the mill, payments on the mill if he has any and if he's only selling a hand full of parts to a few every now and again his mill damn sure isn't paid for. Oh but I forgort he can vacuum up the scraps and same the waste and get $.65 at the metal recycler but I forgot that 3 dollars he made was spent in wear and tear and gas for his truck/car.
My wifes cousin had a small shop in Atlanta with a large machine center he leased new. His lease on just the machine was 20K a month, he made a good living but had the thing running at least 18 hours a day everyday for over 5 years. When he got sick of killing himself and not having a life he quit and got a job. The mill got turned in but it had so many hours on it he had to pay 75K to get out of the lease.
Last time I bought endmills I spent right at 1000 dollars and could hold all of them in one hand.
Most of the custom parts you see pop up on the forums are built by guys that work in Fab/machine shops and there using scraps from there bins to build there parts. Nothing wrong with using a drop from a larger part but 90% I'm sure aren't buying the metal all your paying is shipping and there time to use there bosses stuff just like your buddy will be doing I'm sure.
Now for you that don't know to get a part made someone has to design it, draw it, do a prototype run and test fitment then go into production unless its a one off then they do it test and its done. Some times jigs have to be drawn and designed to hold the blank to go into productions for odd shaped or delicate pieces that can't be clamped. If its something simple thats what happens but important things have to go through analysis, stress, strain, FEA software needs to be run etc. Most industrial machine shops charge big for this around here drawing up something after you take them the measurements is $125 for a simple widget complicated things with partial arches, steps etc are way more. Then there set-up time on the mill minimum of one hour then running the part minimum one hour so to go into a shop and say I need a brake bracket set made would probably be 125 to 150 just because one off bs is a pain in the ass. If you want a production run the prototype is going to be around 400 just so if you back out they'll still make something for wasting there time. Then they'll charge you per set of around 60 or more for less than 50 then 50 to 100 is a price etc.
The jig I use to make the gauge panel I sell on here I cut from a 6061 block and allows me to slide it in close it and lock into position the I run 3 different programs unless its has the serial port then its 5. The jig took 4 days to design and cut to get perfect but alot of that was just manual cutting measuring and not alot of code was run.
So before you start bashing on the builder and what he charges remember what it cost him to build your part and stay in business.