My guess would be that Hamilton Wanderers have the smallest budget as they are a provincial club and unlike Southern United they are totally independent of, and do not have any financial backing from their local football federation.
While there is backing from the local federation, at least being a local club allows Hamilton to have a connected membership and provides a basis to fundraise. SU is dependant on grants and sponsors which have been largely one off in the past (hence now partnered with FS). I would hope a local football club could raise more throughout a year through its membership than SU has in the past through grants and sponsors - but it agreed that it would be a lot less than the rest