It's not just for ESO+. You can gift it for that price. I kinda know your pain, as I bought one slot for gold last week so I overpaid about 100k gold.
"I bear the cruel weight of certainty. Total, absolute, relentless certainty. People rarely comprehend the luxury of doubt... the freedom that comes with indecision. I envy you."
―Sotha Sil
Yeah it got me as well. I bought 1 character upgrade slot after debating it with myself for ages. I finally went ahead and spent the crowns. Then the next day the sale happened. It's only a few 100 crowns difference, but still quite frustrating.