I had Quantum Radio Slaves from back when they were like six hundred bucks. But they're HUGE...
I got a cheap "Yongyou" Chinese set, transmitter and two receivers for like $25 - they fire reliably with my SLRs, DSLRs, 35mm RFs, 4x5 and my Sekonic meter. But I have 7 RB lenses and none would fire with it, nor would my older Spotmeter (Minolta F).
So I got a first or 2nd gen Pocketwizard set on eBay for like $65. Compact and works with everything, happy camper. Much better range than the cheapies, which will fail if they get behind a pack or a stand. if I need more receivers, I believe anything from the PW line will work with what I already have. Good professional system.