All I know of offhand for mobile robots is the Kiva system, which Amazon purchased last year. The company, I mean - Amazon purchased the whole Kiva company. But they still support other clients. (Gilt, Office Depot, Staples, Crate & Barrel, Toys R Us, and Saks Fifth Avenue.) I suppose it's possible to remove the pallet lifters, install pushers, and repurpose the control software. I can't find any information on cost, beyond "millions." Sounds like most Kiva customers use hundreds or thousands of the units, rather than one or two.