You would only charge $12.50 to mount it? why so little, I would be at least $50 to mount it with our rolls roller. by the time you load the sheet on the table, align the print, mount it and trim the excess you would loose money at $12.50, not to mention if the client chooses to do away with the laminate on the 2 mil it's like applying a wet noodle, way more likely to mess it up and need a reprint, on your dime of course.
I agree, you are most likely right on point. However, the truth is, we have no set pricing for mounting prints on customer supplied substrate so I pulled that number out of my arse based on how much I would charge to mount a print to our own substrate, which is probably still low but it keeps us competitive with how we price our substrates and prints. All in all, it's about a 5-7 minute job with an application table and even though we probably should charge more we just don't. The table pays for itself every day just with laminating prints alone.
I think I tend to look at the mounting capability as an added bonus, since we used to mount prints by hand and charged accordingly (closer to your $50 price point) but then we ended up pricing ourselves out of a lot of jobs that way. Now with the table, I can mount and trim at least eight 4 x 8 panels per hour, so $12.50 per panel doesn't seem all that bad, but I get what you're saying.
I used to feel the same way about mounting unlaminated prints but as long as they are completely outgassed and I work from the center out, I've never had an issue.