AC System 2004 Lincoln Aviator

I took my Avaitor to dealship have AC blew out freon for second time in a few weeks. They stated The system was building pressure and blowing the freon out. They also stated that for $2600.00 They could fix the problem. $2600 is a fifth the cost I paid for the car 2 years ago. Its outrageous. Anyway, They said it was so costly because the entire system had to be replaced. Its a dual system so two of everything except compressor. They diagonosed this by from my understanding using some kinda pressure gauge. They didn't use any dye etc. Can it be fixed without replacing the entire system? Can they dye it, find leak and just fix that part? Someone told me the entire system must be replaced cause air gets in system and then I don't know. Must be a better/cheaper way to get it fixed or do I just need to "bite the bullet" on this one. Thank you so much in advanced. The advice herin on the website is priceless. Thanks