What's UPS going to charge you for a letter? $10?
Let's suppose we lived in that world. It's 2036, and sending a letter costs $10. Are you better off than you were in 1996 (when it cost 32 cents), or worse off?
We might be better off. Sure, it costs thirty times as much, but you might be having to do it less than a thirtieth as often. I'll admit my memory is foggy, but I'm pretty sure that every damn month I was having to mail multiple bill payments. That crap is over, and we're all happier for it, aren't we? Nowdays, I'm snailmailing infrequently enough that I don't even know if it's something I do twice a year, or once every two years, or what. It's getting hard to measure, but one thing's for sure: it ain't much.
$10 for a letter would be ok, if you almost never had to use it. And aren't we heading that way? Isn't nearly every instance (I'm trying to be open to there being some exceptions, though I'm actually drawing a blank right now) where you can't use email, a situation where you view the requirement as being a consequence of someone else's fuckup, incompetence, anachronism, etc? (e.g. this AC's idea that "my financial records where I need physical copies for tax audit purposes" is a feature of snailmail, rather than a defect in government's information-provenance-verification procedures.)
I'm not even necessarily advocating the death of USPS. Maybe they'll "rightsize" to fit the country's communications needs, such that they are the ones charging $10 to deliver a letter. It wouldn't be so bad, if overall, we still end up spending less.