If you do this a while you will find that it is possible to build up a decent coin collection for free. I remember reading in an article or book how people used to get rolls at a bank and sell them making small profit that they would put into their collection or buy 4 proof sets and sell 3 at a profit and basically keep one for free. Lately you may have noticed that it is possible to snatch up popular mint products before they sell out and resell them for a decent profit (2011 SAE set and Army commem half for example) and roll that money into your collection. If you are astute you may be able to build a nice collection for free.
I think that a nice collection can be built for free, it may take some time though. I have come across many silver and proof coins in my change over the years, they are becoming far a few between but I still find them from time to time.
It depends on what you call "for free". Time is money for me. Thus, I'm not necessarily into sorting through a million coins to find a few that have value. It is more fun for me to find good deals on ebay, local auctions, and coin shows. It seems a little more like skill than luck.
