dogs eyes

I have a chocolate lab and he has developed a big brown spot below his pupil it is getting bigger and one eye it is going into the pupil my vet is going to look into is eye with a light he suggest us to go to a specialist but it could cost up to $3,000 they have high tech stuff he don't act any different he still can see but i am concern in the long run. If you know about these brown spots please let me know .thank you .....Jan