Sounds like a job for the Prestige mechanic.
The two do rather go hand-in-hand, but from my reading, Prestige is presented as primarily focused on mechanics, from the player's perspective, designed to get something
special that would be
abnormal but not impossible for them to obtain... relative to their current Prestige.
Billing your traveling expenses back to your Stage-4 Stronghold in low-Tier regions (the likes of which I intended to anecdotally describe in my previous comment) struck me as something that, historically, was the norm (for people with Strongholds and, yes, Prestige), which is why it didn't jump out to me that it would be a valid use of the Prestige mechanics.
Then again, while there's nothing in the rules that explicitly identifies it, this is the kind of thing I'll probably rule at my table as being obtainable under the concept of "Passive Prestige" -- things that, in the party's past, would have required a Prestige check because they were, at that (lower-Prestige-rating) time, things that were special and abnormal but not impossible to obtain, but as a result of the increases to their Prestige, are no longer appropriately categorized in that fashion.
Take your typical house for instance. Spending the cash to buy a halfling shire house doesn't give you the inherited wealth you need to keep your larder filled and pay a gardener.
Well, no, but specifically the Halfling Shire House (Average quality, which I personally equate to a Moderate lifestyle) is underground, but such shire homes are described in the Culture segments as being
just underground, meaning that the house also has potentially useful land on top of it. Under the conceit that (unless otherwise needed for narrative purposes) the homeowner has secured competent staff, who are able to make use of the
whole stronghold to good effect, I don't find it unlikely that a staff of three (Gardener, Cook, Housekeeper) would be able to make arrangements for the stronghold to support an additional 1.5 gp per day cost (at least while the owner was in residence) above the ability to support the three of them properly (if that was called for, even -- maybe they're not live-in, and the maintenance costs are low because in the grand scheme of things the staff's needs are being met as a result of their pooling of resources with their families or something).
The "House" strongholds, and the smallest "Castle" strongholds, are the only ones that seem to me to present this kind of an obstacle to sustaining themselves; all of the other strongholds have fairly obvious mechanisms for revenue generation, as I see it.
The "how" of each instance where such an answer is needed is part of the narrative-crafting experience, in my view. Some groups would find that kind of content unnecessary; others will find it fascinating. I feel like there's enough in the core rules to provide a solid foundation without being more complex than it needs to be for the majority of the target audience.