How much does it cost to fix a oil leak on a 2004 x3 bmw?

depending on if you go to BMW or have a friend to do it.

If you have to ask, you can't afford it-

The most common leaks are form the Oil Filter Housing and the Valve Cover Gasket. Your dealer will want to replace the entire housing. DON'T PAY FOR THAT! If they won;t just replace the gasket, take it to an independant. It should be about a 1.5 hour repair, or less. The Valve Cover is about the same cost. It's just a gasket replacement. Both of those repairs you can do yourself, if you're mechanically inclined. But be extra careful to get the gasket in correctly or you'll make matters worse. Good Luck!