You need to have more information. E.g., what condition are the bills in, are they Federal Reserve Notes or Silver Certificates, and what is the series letter (if any) following the date?
Look at a site such as http://www.uscurrencyauctions.com/prices.htm for price guides.
By way of explanation, the date on a bill is not the same as the date on a coin. The date is changed only when there is either a redesign or a change in Treasury Secretaries, and sometimes not even then. Normally a minor change is designated by a letter after the date. For example, the 1935 design for $1 bills was used well into the 1950s, so you saw bills with dates of 1935, 1935A, etc. all the way up to 1935H !