A round trip that costs $600 (figure $0.50/mile) is just stupid business. It is almost always cheaper to fly and rent a car for any trip over 400 miles. Not to mention that is is safer to fly than to drive. They should have specified in advance what the terms for your travel expenses would be. If they were really on the ball, they would have made the hotel, car, and plane reservations for you and paid for them.
Send in the form. Frankly, if that expense scares them off just think what it will be like working for them. Starbucks is the only place for bean counters.