I remember, Alex, that you've said that orbital arrays are cost-free for now. So here's my (very unoriginal) idea for a maintenance cost: metal.
It would work like the fusion lamp, but with metals as required commodity instead of volatiles; this could be worked out in-universe as micrometeorites, solar flux etc. doing one hell of a number on immense, ultralight metal constructs hanging around in space entirely unprotected. As supply becomes insufficient, the market condition would increase hazard back to about half-way of what it would be without it. Metal is also (relatively?) easy to get a hold of in sufficient quantities provided you have a catalytic core (unlike transplutonics). Possible reasoning the hazard wouldn't go past 50% of what's offset: the more holes there are in a thing, the less stuff can hit it.
The only issue I can see arising here is that some core worlds markets may get an increased hazard if there's no pre-existing market capable of supplying 10 metals, which could have knock-on effects throughout the sector's base economy.