There's one option that could cover both the uses mentioned in the OP, but it's not all that "cheap"
Savage Model 24:
Rifle top barrel, shotgun lower barrel

http://www.gunsinternational.com/Savage-Combination-Guns.cfm?cat_id=574
Savage Model 24:
Rifle top barrel, shotgun lower barrel
http://www.gunsinternational.com/Savage-Combination-Guns.cfm?cat_id=574