According to reports Kevin Federline is working with ex-wife Britney Spears so that their young sons can spend time with Spears on tour -- but the family togetherness might come at a price.

Federline wants Spears to pay him for each tour date that Jayden James and Sean Preston attend, says a source with knowledge of the ongoing custody negotiations.

The price tag Federline is putting on quality time with mom: as much as $10,000 per city.

A rep for Federline didn't comment, but a Spears source said, "There is no way he's going to get that kind of money, if he gets any money at all. She's got good people on her side. She's not going to be taken advantage of."