Best Primer/Sealer to get rid of Cigarette and Cat Piss smell

[Cam Jimmy]

I am under contract to buy my next Brrrr, but this one has such a strong smell of cigarette smoke and Cat piss (in some areas). Ive used Kilz 2 before on my other property and it worked OK, but this one is way worse. Someone mentioned BIN shellac based primer for getting rid of strong smoke smells, but its twice as much as any other primer. Has anyone used this stuff before? Any other suggestions? Thanks!