[Just Smokin' Around]

Your price seems high to me. $15+pp for pulled pork with 2 sides and a drink is a little high. I can go to a BBQ joint and get a pulled pork platter with 1 or 2 sides for a lot less than $15. Search around the internet and look at what other BBQ joints charge for catering (look for links in the signatures on this site).
You priced it by adding your profit in the beginning at $6pp. Plus, $2 pp to bring your pit. Have a price to bring your smoker separate from the food cost. You can deliver and serve food without having to take the smoker - warm up ahead of time and use Cambro's.
You should calculate all of your cost first. I didn't see cost of buns, napkins, paper plates, forks, cups, etc. Don't guess you have $50 in misc. item, cost it all out; otherwise, you may leave yourself short. Figure the cost of each side. $1.50 is probably okay for sides. You need a per person price with a minimum of xx people. Suppose they want to do it for 20, 40 or 80. Your profit will be based on number of people, not flat rate per event ( $300 in you example).

Example:
Your cost of 2.30 / sammie sounds about right - 2.50 with bun, plate, napkin, fork.
Side cost vary but 5 lbs tubs of potao salad and cole slaw and large cans of beans plus a little fixing up before you take it - no more than .50 per serving per side.
Tea and lemonade are cheap - .15 per cup plus .15 for the cup ( the cost of the cup is more than the drink ).
Your cost= 2.50 (sammie) + 1.00 (2 sides) + .30 (drink) = 3.80 pp x 50 = $190

If you charge 9.95 pp delivered and set-up on tables = 497.50. At $9.95pp, your gross profit is $6.15pp x 50 = 307.50 gross profit
Some say a general catering rule of thumb is cost times 3. 3.80 x 3 = $11.40pp. Gross profit = $7.60pp ( x 50 = 380 gross profit )

I say gross profit because you have overhead cost for transportation, tables, canopies, equipment, labor, etc.

Pit on site = 150.00 for 4 hours; $25 per hour after that or use a flat rate of 150. Hauling your pit can be a pain to get into a park, backyard.