Pyandonean was already in crates. Sapiarch was in the store I think. Psijic, no idea.

If you want to spend bucks rather than ingame gold, I'd recommend you to buy crowns, sell those for gold and buy the motif with gold. 400g for 1 crown is the current exchange rate in Tamriel Crown Exchange, so if you go into zone, try going lower or equal than that but definitely not higher.
Also be sure to take screenshots of your chatlog and such to get evidence in case you get scammed, which support should help you with. Of course you can try to exchange the crowns directly for the motifs by whispering the players that put them in the guild store.

I highly doubt those motifs will be more than 6M gold together, which is "just" 15 000 crowns. It wouldn't be more expensive than if they went into the crown store with a margin of error of about 3k crowns. It's also safer than trying to gamble for them.

1. Those motifs cost almost nothing now as they've been around for a year
2. You can sell crowns for gold now as the other poster said