Buick LeSabre Forum : “What was the MSRP on a 77 Buick La Sabre Custom?”

contact dealer on this one.

Probably around $15k.  If you have the VIN number of the one you are looking at, you can order a package from GM Historical services that will give you build sheets, original price, etc. for your specific vehicle.  It's well worth the $70 or so that it costs.