They paid about $50k for ch.at. I have a single letter country code domain (3 characters total, x.xx). There are still some single letter country code domains available to register, you could get one for under $1k USD if you want one.

Here’s a reseller with a variety: https://1-single-letter-domains.com/

These guys run a bunch of services on x.xx domains: https://o.ee/services/ like c.im, r.nf, p.lu.