I would have thought about putting some money into it if it were not too high, I think a little cash for the hack for all the time placed into it is not too much to ask. From what I can see in the pictures, it is a very nice hack and would be well worth a small fee of some sort.
My thoughts, it is his hack, if he wishes to release it for free he will do so, if he wishes to set a small fee on the hack, he may also do that. There is not a problem with doing something like that, take the ever popular karma hack for instance, would you really expect Overgrow to give that away for free?

(of course, everyone can wish, but I don't think it is going to happen with all the work that went into the hack).
If you are not willing to pay a small price, you probably do not need the hack anyway, again I will refer to the above mentioned karma hack.
(Note to members/mods/admins - I am not refering to the karma hack to stir up another 20 page long thread, I am simply using it as a reference)