Be sure to use the non-vex resources that are available and legal.
McMaster-Carr has the best prices on most aluminum standoffs (escpecially the long ones), just be sure to search for the right ones (aluminum, female-female,1/4" hex, 8-32 thread), and don’t get a non-vex length.
For a wide variety of legal stuff at good prices, including plastic, wire management, pre-cut 1x1 angles, high strength lock bars, fasteners, cables, and tools, look at www.robosource.net
For pneumatics (if you’re ordering a lot), www.radwell.com has parts, but you have to search by the SMC part numbers, for example https://www.radwell.com/en-US/Buy/SMC/SMC/US14227-S0400 is an air tank, https://www.radwell.com/en-US/Buy/SMC/SMC/NCJ2D10-200 is a pneumatic cylinder, etc. Sometimes there is surplus part available at a discount.
Anti-slip mat is at Lowe’s, Home Depot, etc. Fasteners used to be cheaper from industrial suppliers, but now VEX has a good deal on their star screws, and it’s hard to find anything cheaper, except nylock nuts (from McMaster or Robosource)