W140 Air Conditioning Problem: Help!

My W140 A/C is not blowing cold again. About a month ago, a local repair shop said I was low on coolant (freon?) and recharged me. I was good for about 2 weeks, now it's back to cool air, not cold. The repair shop said I probably have a leak and that the repair is $3000 + because they have to take the dash out more times than not with this problem.

Any ideas, recomendations???? Thanks!