For what it’s worth, you could pick up a second-hand USB audio interface for around $50 (probably). There’s also the Zoom H1n, which would all you to monitor the benjolin as well as record stuff. It can also function as a basic 2in/2out USB interface.
After some googling, I found this kit headphone amp kit.
I’m planning on building it up for use with my incoming benjolin. Ideally, I’m hoping there’s enough room inside the Benjolin box for me to mount it inside. Otherwise, I can always mount it in a standalone box and use it with any other headphone amplification needs.