I'd tell the player to burn in hell for making my life so difficult.
and then I don't know if it took up two slots that there were normally only one of like amulets, and hats, then I'd likely divide the cost by 2. If it took up a ring slot and a glove slot I'd divide cost by 1.5
If it took up one glove slot and one bracer slot instead of being gloves and bracers I wouldn't even reduce the cost since the player is already designing new items he could just build another glove/bracer item for the other hand getting wo items for two slots.