Esav said it already, but do not buy to amass a collection. The only you will make money at that is if you buy high dollar customs from established makers, which will make the pieces already pricey before you even own them. The other way is to buy antique pieces, and there are so many fakes out there, that sometimes the knowledgeable dealers might have a hard time discerning the real stuff.
I started out with Chinese/Pakistan junk. I moved up to Camillus, Cold Steel and CRKT, with some Gerber thrown in. Kershaw, SOG and others filled in along the way. Now, I'm primarily into Benchmades and Spydercos, and plan on moving up to Sebenza and Strider, or will take a left turn into customs.
Most of my collection has either been sold or given away. I gave away the ones that meant something to me to an extent, so I did not really lose any money on those. I am losing money on productions I have bought. Poor judgement and research on my purchases. I was not buying for my needs, just what looked neat, and neat steels/handle materials. Theres nothing wrong with buying what you want, but if you are on a budget like I am, you really have to put in some research. So, Esav was right, buy what you will use. Due to monetary constraints, you can't automatically go out and buy Spydercos, Benchmades or 100 buck plus knives. Buying the quality and design of the knife, as opposed to the brand, is best. Any brand can have great, or poor steels and handle materials. Search the forums here for blade steels. Off the top of my head, production stainless steels to look for are 154CM, ATS34, VG10, S30V, AUS8, 440C, ZDP189, H1 and BG42 (or is BG42 a custom steel, same with ZDP189?). Even carbon steels, like D2, M2, 5160 or 1095.