Coolant leak, 02 Buick century?

roughly intake gasket, coolant, oil change $700-800 less if you do it yourself, give yourself a day or two

You clearly have a coolant leak, and since I assume you are not seeing puddles of coolant on the ground, it must be inside the engine. This is not good because coolant is not a good lubricant. If it gets into your engine oil and is not rectified quickly, the engine can seize. Get it fixed right away to avoid any further damage to your engine.

A leaky intake manifold gasket is a very likely cause of the problem. There are other possible causes (e.g. blown head gasket), but you would have to remove the intake manifold to fix those anyway, so starting with that isn`t a bad thing. Once the intake manifold is removed, the leaking coolant should be obvious to the mechanic, and other possible causes can be checked at that time as well to make sure you don`t have to do it again any time soon.

This is not a hard job, but does take some time, and a bit of knowledge. Less than $100 in parts, but a few hours labour. I guess between $500-$600 to repair. Way cheaper to do it yourself, if you are willing to take your time. I say - get a repair manual, some cheap tools, and give it a shot!

Good luck!