As said, identification becomes an issue once you grow beyond the point where everyone knows everyone else in the unit. Whether that takes a custom uniform or merely an identifying band or patch again depends on scale, finances, and expectations. If you're out in the field getting shot at, it's probably a good idea to be able to identify other members on sight, so a common color (different from the enemy's) or general style makes sense, and a reasonably professional looking unit badge, patch, or band prevents claims of "spying" out of uniform. If you're on parade, hired to keep the population from getting funny ideas about doing a better job of running the planet than whoever is paying you, then you want to look professional (your employer may even expect it), and that requires uniforms, at least for the more visible elements of your group. Whether that extends to support personnel or not is more likely to be an internal matter.
While "proper" military camos plus parade dress uniforms can easily add up to the listed 300 C-Bills or more per person, having matching "military-looking" shirts or jackets and the same color pants is more likely to be in the 100 range. An identification band or patch, ideally worn on a shirt or jacket of more-or-less the unit's chosen color picked up at local stores, is dirt cheap. If you can't even afford that, then your unit is probably running out of food as well as ammo, and it's time to consider looking for another line of work that pays the bills. Of course, your group may have consciously decided NOT to wear uniforms, and the absence of uniforms of any sort in a situation where everyone else is wearing one can be a mark of identification to some degree.