When the head gasket on my daily driven 2.8 S10 went, I was quoted $1300

. Ended up doing it by myself (first time I ever took a set of valve covers off) for less than $200. I don't even want to guess what the labor would be for a syty. Either way, water/antifreeze mixing with your oil will do BAD things to your bearings in the long run so don't sleep on it for too long. Not to mention if you have a catastrophic gasket failure and hydrolock your motor. If water enters your combustion chamber and the motor tries to compress it, VERY BAD things WILL happen... HTH's
Mike Campbell