Thank you Enzie, Michele for your replies and good suggestions. I did a quick search through my phone book for prices and unfortunately discovered UHaul does not do unlimited mileage here. I need to dig out the calculator (as well as the tape measure at the van) to see what the best way would be. Another idea I'd like to investigate is the cost of shipping the painting, and meeting it there.
Enzie, the painting is a commissioned full-length portrait in a landscape. I love to work large, it accomodates my need to 'plunk the paint around'. Fortunately for me, the client agreed (in this case) that bigger is better.