I split this topic off from the Costco glasses thread
because I wasn't sure that you were specifically asking about the costs at Costco or places in general.
I'm actually scheduled to have my annual eye exam at Costco later this week - my first time getting my eyes examined there. I'll check out the prices and options on the 1.67 photochromic lenses there.
Looking at Zenni Optical's website
(the cheapest I have found for regular lenses / frames - and you can read my review of Zenni here
) it says that their 1.67 index lenses start at $34.95 and the photochromic lenses are $27. Unfortunately, when you combine things, they are not just added together. I went to do a pretend order on their site and under prescription and lens type options there were numerous choices that involve photochromic lenses. The one you are interested in is the 1.67 Transitions VI Photochromic single vision grey - which adds a whopping $169 to the cost!
If you just wanted to add photochromic to their standard single lens, it would only add $19. I am guessing the main reason for the huge increase in cost is because they use the name brand Transitions photochromic lenses on their higher index lenses.
Hopefully I'll remember to ask at Costco and I can let you know how much extra it would be there.