We have an older pontiac sunfire 2001 that suddenly lost the airconditioning from last summer to this summer...possibly during some of the really cold winter months we had here cracked a line or something?

I talked to my mechanic today and he said it could be up to $1500 to replace the evaporator, or - he could use a seal product from Canada and charge it for under $300...but he was going to put it under 50% charge tomorrow and make sure the leak is on the high side and not the low. If it is on the low side, he will charge it so we can use it this summer (or the rest of it), and then next spring sell the car as planned without it working or at least with a disclaimer that it will need recharged regularly.
So my questions are: Does this all sound right? What should I do?