I am not sure why sealer is not good ? It is just a heavier grade oil. If the leak is in the evaporator, and if you cannot do the mechanical/electrical work yourself, and if you want it to be fixed perfectly, then you will have to pay upwards of 3K for the repairs no matter where you go.

I would take the car to an auto air specialist (not a general purpose mechanic) and get a diagnosis and an estimate from them. You have to spend this small amount to make a wiser decision if the costs are going to be around 3K. As many have said, you may not have a leak, dealers just want to give you the worst case estimate, and the attitude of that dealer is very suspicious, as if they just did not want to work on your car or wanted to cheat you.

If the leak is behind the dashboard but is a small leak, auto air place may recommend stop-leak or something which is a heavier grade oil. The a/c system is sealed by oil and o-rings, and heavier grade oil just seals it a little better. And the system may be sealed good enough for refrigerant to last a few months. R134a is not very expensive and if you have to do this 2 to 3 times during summer, you would have a genuine alternative to spending 3K.

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Saumil S. Patel