Solved by: @dm

TL;DR:

• pick name such that characters 17th through 20th correspond to the flag printing routine’s address 0x8048878
• pick prices such that the node for the item you named moves to the root of the tree that stores the (item,price) entries

Original writeup (https://dm248.github.io/posts/20200725_UIUCTF_AccountingAccidents).