Rex needs to be in Boston by noon Tuesday. The problem is you live in New York and it's currently Saturday. Shipping pets by plane is not a new phenomenon, but it has become a more convenient and cost-effective way to get your pooch from point A to point B.
How big is Rex? Per Delta Airlines, if Rex is in the bull mastiff/Great Dane range (very large), the cost to ship in the United States is in the range of approximately $700. (Additional charges may and probably will apply.)
Continental Airlines requires a "Live Warm Blooded Animal Acceptance Checklist," which states that health certificates, permits, licenses, 16 oz. or less of food, a leash and collar are necessary prior to shipment of the dog. Contact their Live Animal Desk office at (800) 575-3335 for actual shipping rates.
According to American Airlines Cargo website, AACargo.com, dogs cannot be shipped to the United Kingdom, China, India or any destination more than 12 hours away by plane. With that being said, Rex's ticket from Boston to New York will set you back roughly $200 assuming he weighs 11 to 25 lbs.
Not all carriers will "ship" your pet or even allow it in the cargo bin at all. Southwest Airlines only accept in-cabin cats and dogs at a fee of $75 each way. Be advised that Rex counts as a carry-on.
Northwest Airlines and many other carriers will not ship a pet under any circumstances if the temperature will rise above 85 degree F at any point during the flight. If Rex is flying in the lower 48 states, such as from Boston to New York in the spring, he should be just fine. The cost of his ticket would run about $350 if he fits into the 50- to 70-lb. category.