I have a system similar to what has been presented above. I got my vacuum pump at an RC auction for real cheap; got the vacuum switch on eBay for about what APC charges, so no great bargain there; got three vacuum gauges off eBay for like $5 apiece, only because no one else was bidding at the time; 4" pvc pipe w/ capped ends reservoir; fittings & tubing from mscdirect.com, which has a pretty good industrial supplies website, good service, fast shipping, more convenient than getting stuck in traffic to go to the store.

Studying the ACP site a few nights ago, I almost think you could do without the vacuum switch and just use their APC relief valve, which closes at 8 psi, opens at 10 psi, values for white foam, which is all I ever work with. The relief valve is simpler and cheaper than the vacuum switch.

I have not found a better source than ACP for the usual supplies, bag fitting, seals, etc. They're good people to deal with imo. Get their video if all this is new to you.