Twice-daily Vietnam Airlines flights connect Hanoi to Dien Bien Phu; the one-way fare starts at around 1,000,000d. Consider flying to Dien Bien Phu and returning to Hanoi via some form of ground transportation, either down Highway 6 or up to Sapa and down Route 70 and back to the capital on the Noi Bai-Lao Cai Expressway. Talk with one of the travel agencies or tourist cafés in Hanoi to see if they have contacts that can book you a one-way trip back to the capital. They may insist, however, that you pay for the mileage for the driver's return to Dien Bien Phu or Son La.
Vietnam Airlines. 024/3832–0320; www.vietnamairlines.com.