1oz kookaburra 2010 priced at $29.95, page-24

IMHO you should buy coins as close to their metal price as possible. If buying from a dealer or mint, the more you buy the cheaper so buy in bulk. If your only buying one or two at a time, and you want to get lots of different years/types then the secondary market e.g. ebay is your best bet. We are lucky in Australia that there are so many great quality silver bullion coins.

That said, buying coins isn't really the best way to invest in silver (e.g. it can be a somewhat illiquid investment), but it's quite fun.