This weekend commemorates the 100th Anniversary of the sinking of the Titanic. Union Station in Kansas City has a current artifacts exhibit on display (through Labor Day). This weekend, however, you can get in for only $4.15! The regular admission rate is close to $20 a person. This offer is valid only on April 14th and not through on-line purchases.
Update: It appears this pricing is only from 8 pm – midnight (the source that provided this did not include this information — sorry folks)!