If you're ok with a slightly rougher finish on the casting but the same material properties as Kee Klamp, you can get cheaper store-brand variants of many of the common connector types from Global Industrial, Grainger, and other industrial suppliers.

Also, structural pipe is usually pretty dirty from production and I've found it's worth the cost to just have a local metal fabricator take care of the cleaning.

https://www.globalindustrial.com/c/storage/fittings-framing-...