Other than Primal, Barbaric, Daedric and Ancient Elf:

New Moon is pretty cheap and easy to get pages for. I’m not sure about the holiday pages (Skinchanger, Hallowjack) anymore; for Hallowjack you might be better off looking for old Witches Festival Writs and completing those. And there are some Motifs like IIRC Dremora or Assassin’s League where some pages are trivial/cheap to find but others aren’t because they drop from different activities.

Really the easiest way is probably to check your local guild traders and just buy everything you don’t know under a certain price limit, prioritizing Motifs you’re already close to completing.

Buying from the crown store is almost always the most expensive way to get a motif (if you use the crown:gold exchange).

You can either search guild stores for the cheap ones (like Celestial, New Moon Priest, etc...)

They will get significantly cheaper in April with the anniversary event when motifs drop like candy.

Alternatively, you can just create a new character and learn the base-game racial motifs on that character. With Account Wide Achievements it makes the "learn 50 motifs" for GMC trivial, as you can just learn the base game motifs on a few characters and get it for the entire account.