All right. It really isn't that bad, but I do enjoy cleaning ancient coins.
Mention "cleaning" to collectors of modern coins, and you will get some interesting reactions, anything from shocked silence, to the threat of imminent violence.Cleaning modern coins is a strict no-no. Even a light buffing to bring out the shine can greatly reduce the value of a modern coin, and don't even think of asking if you can take a modern coin out of it's flip or slab to get a better look at it. The oils from your skin will smudge the poor thing!
Not so with ancients. ALL ancient coins have been cleaned.
Cleaning coins is fun and relaxing, and it can be a good way to add coins to your collection, but it is not the best way to build a collection. This is because most of the lots of uncleaned coins offered for sale have been picked over for the best coins. Even if the seller that you buy from is able to resist the temptation to remove the best coins, the lot has been through other hands that are not so reluctant to pull out any coins that look like they will be higher grade.
If you buy uncleaned coins, buy them for the fun and challenge of cleaning them, but don't buy them with the expectation that you are going to find rare, high grade silver and gold coins. Cleaning coins should be done as a hobby, not as part of your retirement plan.
Spend some time looking around on the eBay or Yahoo auction sites, and you will see a number of sellers offering bulk lots of uncleaned coins costing anywhere from 0.50 - 2.50 each. As a general guide, the really cheap coins are often culls from dealer's lots (sometimes called "floor sweepings"). Buy these coins if you are looking for something to practice on. They can be great for people just learning to clean ancients, but the number of "keepers" is going to be pretty low. I've bought some very nice lots in the 1.50 - 2.00 range, but spending more is not a guarantee that you are going to get good coins. Look for dealers that take a picture of each new lot instead of using the same picture over and over again. This will give you an idea of the general quality of the coins being sold. Check their feedback (if available) to see what past customers have said about the seller.
Start by buying small lots from several different dealers, and compare the finished products to see what percentage of the coins are decent quality and how many are junk. If you find that 50% or more are identifiable, you are in pretty good shape. Generally speaking, when you spend $1.00 on a coin, you are going to get a coin worth about $1.00.
If you want to get some ideas for dealers to buy from, check out Scott Joviel's web site. Scott buys hundreds of coins, cleans them, and puts pictures of the finished product on his site for others to see. I've bought coins from a number of dealers that he recommends, and I've been very happy with the results. You can get to his site on my links page.