AnkerDirect via eBay offers its Anker PowerHouse 120,000mAh Portable Outlet for $499.99. In cart, that falls to $349.99. With free shipping, that's tied with our mention from two weeks ago as the best price we've seen for this model. (It's also $100 under what Amazon charges.) Features include a 12V car socket, 110V AC outlet, and four USB ports.
These companies frequently hire for positions that let you work outside a traditional office environment.