Next is the shipping. Ask the company how they will be shipping the finish prints. Ideally, you want the prints to be laid flat and shipped without damage. This may cost you some money but it will be well worth it.
Most large prints are shipped rolled. A flat 24"x36" print would probably be shipped in a 30"x40" box. That is oversized and with 300 total prints, shipping might total $500. 300 prints will end up weighing a lot. A 30"x40" box gets charged an oversized fee while a 30 inch long tube does not get any extra shipping fee by delivery companies.
Best bet might be to go with a local provider. Where you can work with someone local, spend your money within your local economy (better for your town/area), get a couple of test prints done before you order all 300. If you went with an out of town/state print lab you would pay $20 shipping to receive a couple of test prints instead of just driving to your local lab. Save the $500 in shipping though you'll pay sales tax (again your local economy will thank you) by picking up the prints yourself. Then there's no chance of poor packaging or damage during delivery if you are in control of picking up the prints yourself.