Both are expensive, high-end aircraft - why does the disposable UAV cost more than the manned system?
The Global Hawk is decidely NOT a disposable system; it's meant to have a flying hour lifespan similar to comparable manned high-altitude recce systems, e.g. the U-2. And keep in mind that its pricetag also includes a chem warfare-hardened ground control station van and intrusion-safed data/comm link antenna suite.