rusty bolt

I recently removed my thermostat housing. unfortunatly in the proccess i broke a one of the bolts. the head of the bolt is broke off. after removing the other two bolts and the housing i can see a decent amount of the bolt still sticking out. i think it maybe rust on. i tryed clamping a pair of channel locks on it but it wont grip on tight enough. any other ideas. i cant drive it at all with bad bolt. any ideas on how to romove or at rig it so it doesnt leak long enough to drive it to a shop? if i need to purchase any tools how much might the cost. i dont have a whole lot to spend

they sell a couple different types of bolt/screw extractors. you could also try clamping a pair of vise grips on it, or my personal favorate: gator grips. all of these can be bought at sears and for the most part are not too expensive.