I always try to buy the best I can afford. I think quality not quantity is the way to go with any collection. Rarity need not be at a huge cost, increase your knowledge, find an area to specialise in and you would be surprised at some of the material available. Personally I enjoy English hammered especially early medieval and medieval. There is a wealth of material available in the short cross penny type but it does need a specialised knowledge and lots or research, but that is the part I enjoy most and of course you learn a lot about history too! Most of all enjoy it whatever you collect, buy something because you like it and and you will never be disappointed, well not often anyway :-)