I haven't sold for years but I just looked up the selling help guide as usually fees are pretty straight forward if you look at the information pages.

What I noticed is the fee for promoted listings can vary. The seller seems to decide the % rate.

That is probably why you weren't shown a definite price.

Promoted Listings Standard | eBay

It seems the higher % you choose, the more 'promoted' it will be. Probably worth having a read to see if it would suit your items or not.