Those shotgun inserts Sunray mentions are short (10") rifled inserts that allow firing pistol caliber cartridges from a shotgun. They depend on the fact that a bullet fired from the insert will not touch the host barrel and so will be reasonably accurate. But the muzzle blast from the insert will still exert pressure on the shotgun barrel and, except for small callibers, probably split the damaged barrel further.
Sorry, but there is no magic and inexpensive way to restore that shotgun to firing condition, at least not in the barrel that is split.
Another point I have to ask about. If one barrel split from firing the wrong ammunition, is the OP sure the other barrel is still OK? If it was also fired with that ammo, it could be overstressed or bulged, even if not visibly damaged or split.
Jim