Spencer Pratt & Heidi Montag on 'Celebrity Wife Swap' -- Speidi’s SWEET Payday

Heidi and Spencer Pratt are finally splitting up ... briefly, anyway ... because they are taking part in "Celebrity Wife Swap" and taking home a nice check for it too.

According to our sources, the O.G. most hated couple of reality TV shot an episode that airs next week -- and they'll be swapping with seven-time Olympic medalist Amanda Beard and her husband.

Our sources say the Pratts took home $50,000 for the gig ... which we know is nearly $20,000 more than some other celeb couples have been paid.