What I hadn't known, was that there wasn't much to it in real life: The Pony Express operated from April 1860 to October 1861, when the Transcontinental Telegraph reached Salt Lake City. The original route was St. Joseph, Missouri to Sacramento, but in March 1861 they scaled back to a route between Salt Lake City and Sacramento.
They made $90,000 and lost $200,000. Their business plan was to get a US government contract to deliver mail, but a stagecoach operator got the contract instead. He was a day or two slower, but more reliable and had more bandwidth.
The Pony Express was a high-profile startup that failed, and failed quickly. They were the CueCat of the 19th century. Their technology was obsolete a decade before they launched. I guess Wired discover them any day now. Next thing you know, they'll be the next big thing.