a half pan of beans feeds between 20 and 25 depending on the size of the spoon. Figure 10 - #10 cans with nothing added. If you add 2 cans worth of good stuff then buy 8 cans.
Drop off only? Are you supplying chaffers to keep it warm for 6 hours? If not I think you have a problem with food safety. No way I'd agree to this. I'd insist on being onsite to supervise.
pricing 200 people 2 meats and beans - at least $10 per person and that's on the understanding that it's only one serving per person. When food is gone it's gone. Extra helpings make this closer to $15. I'd take cost of 2 briskets and multiply by 4 and add it to the price. Your meat quantities are a minimum as far as I'm concerned and not adequate for a 6 hour buffet.
Retired competition cook. BBQ mentor.