“What is a collectible typewriter that I should purchase on sight?”

Collectible.

If you mean, a typewriter that I can easily sell off for more than I paid for it and which will probably increase in value in the coming years:

Hermes 3000:

The bulbous Swiss typewriter with the minty green keys guarded by Mingus is a 1965 Hermes 3000, an iconic typewriter and favoured by respected writers and collectors like Tom Hanks, Sam Shepard and Larry McMurtry (who thanked his H3K in his Oscar speech for...