Here's a scan of the prices from the Buick Price Directory, dated 1/2/79. Inflation was rampant back then. Prices on the base car were up $150-200 by April. So these prices are likely to vary depending on what source and date is used.
The SPID label showing all vehicle options and configurations wasn't used on Buicks until '84. The next best thing would be the build sheet if one can be located. Sometimes they were placed on top of the gas tank, under the carpet, behind seat cushions, behind the door panels etc.