Lower intake manifold gasket is leaking

My thermostat has been going all over the place and I took it in to get the coolant system flushed only to discover the lower intake manifold gasket is leaking. The mechanic said I did have a few weeks "at most" but suggested this may be the time I decide rather I'm going to keep sinking money into this car, or start thinking about replacing it. It's been a good car but the last two years repairs are getting pricier and while just getting this problem repaired wouldn't be so bad, from what I'm reading - this could be the beginning of some more serious problems with the entire cooling system as well as the engine. I know trading or keeping is my own personal choice - I guess I'm just asking for opinions here.