Help needed: coolant leak due to head gasket failure? Thoughts?
A couple of weeks ago I noticed a low coolant warning on my dash. So the next day I added some coolant and water to the radiator while it was cold. I was surprised at how low it was. I added just below a quart of fluid. A few days later got the same indication on my dash and did the same. I never noticed an outward indication of a leak (hoses, puddle underneath car or inside at bottom of the plastic engine covers,..). Then this low coolant was happening every day and I was easily adding at least a quart each time. I had only been using my car to commute to work ~40 miles round trip.
On the last weekday, the heat stopped working. It was no longer blowing hot or even warm air. I read that could be due to low coolant, but I also knew that I had a leak somewhere and feared it could be internal - like the valley pan. That weekend I dropped it off at the mechanic's. Funny thing: now the heater was working - it was blowing hot air. Anyway, the mechanic tells me he suspects the head gasket may be blown because he did a pressure test and it held pressure for about an hour. However he doesn't have the tools to fix it.
So I read post while doing my research on here for similar issues and the reference to refill procedures. Also I have a zionsville radiator. so some parts of the process might be a little different?
How do I know for sure if this is headgasket issues, valley pan, or something else?
My main concern is if this is a head gasket work, how much could this set me back? What is a reasonable cost range for doing this sort of work?