first thing you have to do is stop driving it. that's the very first sterp that should always be taken when you suspect a blown ehadgasket, or any other kind of problem you may encounter. Usually driving it will will only make the problem worse. This can be seen with suspension problems, engine problems, transmissions, etc.
So open your radiator and see what the fluid level is like. Look in your reservoir as well, and also look at what color the coolant is. Next would be to take out the oil dipstick and see what the oil looks like, sometime you'll have coolant on the dipstick if the HG is blown. You could also try starting the car and opening the radiator or observing the reservoir. Sometimes when the HG blows it will make bubbles in the cooling system (exhaust gas) and you'll see the gas rising out of the tank too.
If the fire ring (metal ring around each cylinder) is blown then a compression test on all 6 cylinders will reveal it. This is the most common failure. I can go into another cylinder, a coolant passage, or an oil passage, or if you're really lucky, all 3!
A headgasket set from fel-pro is about 100 dollars, plus 30 dollars in head bolts (which NEED to be replaced once removed, because they're torque-to-yield and only hold torque once). If you're novice at engines then it may seem difficult at first. But by taking on the project you will gain plenty of experience with your car and motors in general. A shop could charge you anywhere from 1300-2000 dollars for this job, what would only cost you 300 tops. It involves removing the upper and lower intake manifolds, valve covers, exhaust manifolds, accessory brackets, and of course heads. This would also be a good time to replace the water pump and your coolant hoses.