When the tax has been paid at the time of the recordation of the original deed, no additional recordation tax shall be required for admitting to record:
4. A deed arising out of a contract to purchase real estate; if the tax already paid is less than a proper tax based upon the full amount of consideration or actual value of the property involved in the transaction, an additional tax shall be paid based on the difference between the full amount of such consideration or actual value and the amount on which the tax has been paid; or
Code 1950, § 58-61; 1952, c. 461; 1964, cc. 19, 361; 1970, c. 420; 1971, Ex. Sess., c. 60; 1972, c. 250; 1977, c. 418; 1979, cc. 559, 566; 1982, c. 651; 1984, c. 675.