Bespoke dispatch/scheduling/tracking system

A management system for a courier company which works like a taxi company, an instant delivery service.
Sytsem to take a clients order, schedule jobs (operator driven or system auto allocates), track driver PDA's, invoice cleints, hold client and driver details. A PDA application is required. Ongoing development and support required.
System needs to be deliverd ASAP. Please confirm cost and timescale. Previous experience in building such a system would be good.