Unfortunately, as you discovered, there is no such thing as a discounted one day ticket. Additionally, one day tickets are quite expensive.
The only way you can effectively get a discount is to get a 10 day no expiration ticket. It's a big outlay at first ($481.38, including tax), and it's only worth it if you'll be back for more trips in the future to use the remaining 9 days, but $481.38 for 10 days works out to just $48.14 per day... much better than the $84.14 you'd pay for a 1 day ticket.