First the Megabytes
According to the what I found online, the Prius has a cargo capacity of 21.6 cubic feet. A mid-high level thumb drive is the Patriot 64Gb drive. Product Dimensions: 2.1 x 0.9 x 0.4 inches ; 0.3 ounces. So each thumb drive occupies about 1.1 cubic inches. Allowing for some slack between the drives and not worrying too much about the close-packing problem, that gives us a capacity of 33,931 thumb drives which will weigh 636 pounds and cost us about $1.7 million at Amazon's price of about $50 each. We could probably get a volume discount, though. The Prius has a total payload capacity of 825 pounds, so our driver will have to weigh 189 pounds or less. The total data capacity will be 64Gb X 33,931 or about 2.17 Petabytes.
Now the Seconds
Consider a one-way trip from Washington, DC to San Francisco California (MAE East to MAE west). My road atlas gives 2890 miles (about 21 miles shorter than New York City to Los Angeles). Assuming we have two drivers and haul as fast as legally possible (averaging 50 MPH) this gives us a driving time of 2890/50 = 57.8 hours. This is reasonable, because the winning time in the Cannonball Baker Sea-to-Shining-Sea Memorial Dash is typically under 36 hours.(This is the race that has inspired such cinematic bombs as Gumball Rally and The Cannonball Run) How many seconds is this? 57.8 hours x 60 minutes/hour x 60 seconds/minutes = 208,080 seconds. The trick here is the two drivers. The Prius only has extra capacity for 189 pounds after the thumb drives, so our drivers will have to switch out at fuel stops, pony-express style.
Bandwidth = Megabytes / Second
2.17 Petabytes / 208,080 seconds = 10.44 Gigabytes/Second.How does this compare with commercial internet providers. Apparently Sony makes 2 GigaBit/second internet available in Japan. Give the 8bits/byte difference, our Prius is about 40x faster than that. This illustrates that bandwidth isn't everything, one needs low latency as well to be useful. A week of turn-around time of data going from coast to coast and back isn't very useful, no matter what its bandwidth.