I have this 2005 Aveo the guy at the reily's.

If you have a crack in thermostat housing that should not be expensive to fix depending on what you consider expensive. I just had to repair a leak at my housing but it was just the gasket that seals it down. 15 min and $2 dollars for gasket and I was done.

Yours is likely plastic so there's a good chance it is cracked. Very common for many cars with plastic 1's. You can a new 1 made out of metal for about the same price as a new plastic. I would do that. I see prices on net of about $30 for it. Sop add labor and stuff and you are probably under $75 to get it done depending on shop and area you are in.