As the Headbox II sells for under £100 I presume that is your budget (?)
You might be lucky and find something 2nd hand like Paul suggested but having just been through a similar search (I was after a headphone amp for @ £200) I considered the Music Fidelity X-Can v3 ; ANT Amber ; Gilmore Lite before deciding to spend a bit more

& go for a Meier Corda Aria -
At the risk of similar damage to your wallet

take a trip to
www.head-fi.org which is the best headphone / amp forum in the universe (plenty of threads there on the Headbox II & similar amps) ... Paul