let's see... not exactly low cost but there are alternative options on Amazon, but these are the things I bought from Amazon:
i got my Blue Sea Fuse Block w/ ground (x2), Blue Sea circuit breakers (x2), Blue Sea bus bar. All these have low cost alternative options but I went with Blue Sea since I don't trust cheap Chinese-made key electrical components.
I got my Nilight 5-gang rocker switch system from Amazon. I don't mind the switches go bad since all they do is control the flow of power feed. If they go bad they're not going to cause a fire but 30 minutes of my time to replace.
I also got my HAM radio cat5 extensions and 3.5mm speaker extensions from Amazon too. Those I can do with low-cost MIC since they're inside the cab and not critical to safety.
I also got a Baofeng handheld HAM radio as a backup/ off the truck communication when I spot for my friends. That's a low-cost option from Amazon compared to Yaesu or iCom handheld.