Mitsubishi Mini Split

Hello all. I have a GL12NA. I figured it had a leak in the system as the heat output has been far less than what it normally is. Call a tech out, says it takes 6lbs of R410A. Says they can’t do the leak test for another few days but today he can take out old refrigerant and put in the 6lbs for $1374. Says they charge $587 per 3 lbs of refrigerant.

I was skeptical thinking why would I top this off now if you can’t leak test until next week. Seems like a waste of money. I paid for the service call and the tech left. This price sounded insanely high to me. I start researching and turns out this model only calls for 2 lbs 9 oz of refrigerant.

What should something like this realistically cost? I want to plan for the inside coil needing replaced, it makes the most sense. It sees a lot of moisture in the summer from cooling and also has visible rust.

Any help is greatly appreciated.