Sorry for your troubles and that bummer of a job. That is an absolutely huge leak that the stop leak will do nothing for. In fact, then you just have the stuff gumming up your system.

My dad's car is an E46 M3, so probably not very different from our cars. He ended up paying around $2000-$2200 IIRC. That was from the dealer who originally quoted $3000, but our indy mechanic quoted $1800. The dealer wanted the job as you can see they came way down in price. Unfortunately, the whole dash needs to be disassembled.