Coolant loss/overheating problem-Head Gasket leaking

I have a 2000 V6 3400 engine. I had the intake gaskets repaired with the "good metal ones" according to the mechanic I had do the job. Cost me $600. Car still has coolant leak it overheats every 3 days or so. Leaves no puddles under car when parked. Can smell coolant when stopping at stop light or stop sign or when parking car. No obvious coolant running down or pooling on the engine. Sometimes it seems like smell is coming from heat vents but no wet spots on carpet or liquid coming out of vent. Took to mechanic again and he said it was the head gasket leaking. Wants $1100 to fix it. Don't have the money. Was wondering if any of these additives you can get at Autozone Etc. may work. It wouldn't be my first choice but financially it's about all I can do right now. Any help would be appreciated.

Who diagnosed the intake gaskets? If it was the same mechanic who says it's now the head gaskets, then he either has to make good on it(price on head gasket job, less what you paid for intakes), or take him to small claims court....

Yes he did. Normally he said it would be $1600 but since he miss it be would only charge $1100.