There are several ways you can find the value of old money. Whether old coins or paper money, these are some places that will help you find out what your money's worth.
A quick and easy way to find the value of old money is to do a search using online auction web sites. Look up the money you have in the completed auctions section, if available. This will give you a realistic idea of what it can be sold for. To do this however, you should be familiar with old money, identifying features, mint markings etc, as this can all factor into the value.
Another option to find the value of old money is to take it to a reputable coin dealer in your area. Coin dealers should be able to tell you the value of both old coins as well as paper money. You may want to get opinions from several coin dealers.
You may find web sites with online communities of collectors, dealers and researchers of old money helpful. These people are sometimes known as Numismatists. They may be able to give you values, answer your questions or provide you with information and resources.
The library can be another useful source to find the value of old money. There are several books you can use to research and educate yourself on this subject. Make sure you are looking at up to date values as they do change.