Gem cost for booster packs varies by game. Is there a way for me to see the gem cost of every available booster pack in one window, instead of having to select each game from the dropdown to see the cost? The recently played games list only shows the last six games I've played that have Steam cards.
Unfortunately, no such list exists anywhere within Steam itself.
However, this page on the Steam Trading Cards Wiki attempts to catalog a list of all the different Steam games which have trading cards, along with the gem values for their cards, emoticons/backgrounds, and booster packs. Obviously, this includes games other than the ones you own, so it's a bit of a trade-off rather than a definite improvement. The list is understandably incomplete, not the least because new games constantly need to be added, but it may or may not be helpful, depending on what exactly you're doing with it.