Nowadays, it’s more appropriate to use the IO domain for a tech firm than it is for its intended use - as a ccTLD for the British Indian Ocean Territory. As you may know, input/output is usually referred to as 'IO' or'I/O,' so if you want to be linked with technology, you might want to get an IO domain extension, which is what may have driven its price up.
That said, IO is natively a ccTLD (Country-Code Top-Level Domain) of the British Indian Ocean Territory. When talking about why it’s relatively expensive, while it is mainly associated with tech firms as we’ve previously talked about, the price might have something to do with the fact that it is a ccTLD on top of it being a very popular tech domain extension.
Luckily, though, aside from the price-point, IO doesn’t have additional requirements unlike some other countries where you need to either be a citizen of the said country or you’re required to have a company or trademark (sometimes all of the above), it shouldn’t be that hard to find an IO domain… except for the fact that not that many domain registrars provide IO Domains, which might also be one of the reasons on why it’s price is so high.
The one that I’d like to recommend does have IO domains on offer. The registrar in question is called Nominus and you can find their IO domains here - IO Domains