Personally, I would rather group the subs by functionality and let the editor do the work localising the subs (e.g. Emacs Imenu, other editors have similar functionality).

+1 Or if it has to be alphabetical, what about just inserting them in this order? It's not like you write a new sub every couple of seconds.

But with an amount of 150 subs, there is a good chance they can be grouped in specialised (sub-)modules, reducing the set of subs to an amount that can be managed (read: edit, document, test) with less effort.

Double plus good! Plus you get the alphabetical sorting as ls' default ;)