Deion Sanders -- Divorce Will Cost Him a GIANT House

Deion Sanders is going to wish he lived in a one-bedroom apartment in a bad part of town -- because TMZ has learned a provision in his prenup states the bigger the home he lives in ... the more he has to fork over to his soon-to-be ex-wife Pilar.

As TMZ first reported, Deion and Pilar are ending their marriage after 12 years. According to our sources, the papers will be filed soon.

Sources close to the couple tell us Deion had agreed to buy Pilar a house when they split ... equal to half the value of whatever their current home is. Well nowadays they live in Prosper, TX -- in a home that's almost 30,000 square feet, with 10 bedrooms, 9 full baths (and 4 half baths) ... and a listing price of $21 million.

We're told Pilar has been house hunting since Thanksgiving, looking for a home in the $9-12 million range.