I'm sure this is a big can of worms, but I'd value your opinions on the subject. I'm adding gears to my single speed (2x9) I have mechs, shifters, just picked up a used chainring and I have a nearly new SRAM chain (less than 100 miles). Seeing as I can get a Sunrace cassette for about £13 ,or a Shimano one for about £16... is it worth buying a used cassette just to save a couple of quid, and should I buy an SRAM one to match the chain, or does it not matter