The underlying suggestion behind the silliness is that decent cogs aren't expensive and there's no need to spend huge amounts. You will have to buy a few anyway to you can mess about with gearing, though buying these as you decide you need them is a probably a good plan. For guidance on brands and prices, have a look on Scrod's site and use that as a guide. What's available in local shops is probably a good guide too. Just don't buy el-cheapo because the threading is usually pretty poor and can mess up a hub.