As an addendum... The base/text models which have fallen out of style, are also extremely worth learning and working with. Davinci is still online, I believe, although it is deprecated.

Another lost skill! Learning how things were done before instruct tuning forces you to structure things in such a way so the model can't do it wrong. Half a page of well crafted examples can beat 3 pages of confusing rules!

(They're also magical and amazing at writing, although they produce bizarre and horrifying output sometimes.)