Just doing the math on what kind of revenue a contract this size is going to generate I would imagine there will be a great deal of competition. Especially the large national companies. You really should involve your accountant in your proposal, this can potentially be a half million dollar (or more) a year contract don't you think?
I would look at a lab like Millers that offers all the software etc. you need for order entry and management and figure out your cost of sales, include all your costs, not just lab costs. Like your time, wages paid out to assistants, vehicles, home office, supplies, etc. With this volume you are probably going to hire 4 or 5 (competent) photographers on photo day!
Then calculate what return (profit) you want and you will have a final number to use. This will have wiggle room but you should try to keep a healthy profit margin. Too many businesses offer services so low they end up losing money in the end.
Bottom line is if you cannot make money from it after all expenses are paid then it is not in your best interest to pursue.