Toyora Corolla A/C

Hi,

I've a 1993 toyota corolla. The a/c of my car suddenly stopped giving out cool air. I got the car checked by a mechanic. He said there is a leakage of freon. The mechanic recharged the freon with some dye to find out where exactly the leakage is happening. The a/c worked fine for a month & then stopped giving cool air again. This time the mechanic said he cannot figure out where the leakage is happening & said the whole a/c has to be replaced, the cost of which is $375. I'm not very sure of the actual problem & the price. Am I being taken for a ride?