How set are you on using aluminum angle? Last spring when I started my build I compared prices at Home Depot and Lowes.... and online a few places and the price was way out of my budget for what I needed ( a couple hundred bucks). So I turned to where I usually turn when I don't know something about boats.....here of course and found that a few guys found aluminum angle and square tubing at local salvage/surplus yards. I did some research and found one a little over an hour from my house. I called to see if they carried aluminum stock (angle, tubing,...etc) and the guy said they had aluminum but their inventory changes daily since it was a surplus/scrap yard.
The place was basically a junk yard of surplus material with all types of metals organized according to type. I had a rough idea of what I wanted but I was flexible. They had all types of aluminum ( angle, U channel, small I beams, diamond plate, square tubing, round tubing,...etc.) I spent over 2 hours sorting and picking what I wanted and what I thought I could use. It was sold in linear pieces like a warehouse store and they would cut it to whatever length you needed. Especially if you had to fit it in a car or the back of a truck. Some pieces were over 12ft long.
I tell you all this because the best part was that the aluminum was sold by the pound. I spend around $80 for all of the aluminum material I needed for my build and I think it turned out great. It was a fraction of the money I would have spent at a warehouse store or online after shipping. The only drawback was that it was a little cold outside the day I had to pick the materials as opposed to a warm store or my living room on the laptop. I would do a search of junk yards or scrap yards in your area to see if there is a place like this since I think it could save you a ton of money. Just make sure they have aluminum and sell it by the pound.