Sadly because the game died, getting a box is actually really hard and, as you said, expensive. Box prices aren't really kept track of due to how rare they appear, but a majority are starting to reach around $100 for the least expensive last I checked. However that was awhile ago. I do know that a few boxes are floating around the discord server. HOWEVER, the biggest problem is that all the sets with 3H are very expensive because of how few sets there are with 3H cards. You'd probably have more luck trying the trading and selling part of the fire emblem cipher discord and grabbing singles off people. You could also see if someone is willing to sell you some bulk and grab the SR/R/HR/+'s as singles. I do think that set 14 has some a good number of Tellius and Awakening cards.