I do the same Mikey. I buy quality end mills for great prices when they come up on Ebay, all new and most are Niagara, Putnam, Brubaker,
DoAll, Melin, Guhring, and a few Cleveland. I find the Niagara cutters the best, they come in many flavors, unlike Guhring, which is a great carbide EM, Niagara makes them in HSS, cobalt and carbide. I will never buy used. There are some good deals on Ebay. You just have to watch and wait.
Prices go up and down on tooling, just like the stock market. End mill prices seem to be high right now. More demand? Anyway, check out Ebay and search Niagara end mills.
Dans_Discount_Tools on Ebay has a good selection of new carbide end mills and the prices are very fair. Good seller.