The idea that we need a definitive list of prices for castles, hirelings, mercenary company upkeep, buying an inn or a ship... all the things a rich character could do - well, it might be a useful list, but it wouldn't reflect any particular worlds reality....
If you genuinely cannot put stuff in a campaign for adventurers to spend their gold on once they are fully equipped...
Then you have players who aren't interested in gold outside of what it can buy for their characters. They're out there, it's not an invalid play style.
The key to running for that style is to keep potential rewards on a scale that's relevant throughout the campaign. You can run a campaign about a crew of mercenary adventurers who are perpetually broke, for instance.
You've been mak'n stuff up. Which, if there's a TrueWay2Play 5e, is it.
So you're openly threadjacking. ;P
Seriously, though, the game doesn't support paint-by-numbers DMing. It just doesn't.
What you'd need to get a robust utlity-pricing mechanism is robustly-designed items, and 5e items designs are not that restrained. You'd still need some variation on 'rarity' (as in some items can't be made/bought) or you'd need to scrap existing items and start over.
Since the game doesn't assume items, there's no valid assumption of starting with items, just start at any level with standard gold, y'should be fine.
What you need for an uptime gold sink is something the players care about. If that's progressing their characters within a wealth/level magic-items-expected framework - and with 3.x/PF going on two decades of history, we can only assume alot of D&Ders have acclimated to that expectation - 5e should provide a way to do it. That way can't include items designed in the 5e style, it'd need it's own book of items designed with wealth/level scaling in mind - and, probably, variant encounter guidelines and exp to go with it.
I suppose, for that, you could use 5e items, as well. Anything goes.
It would absolutely mean that, it'd be an inevitable consequence - if not the whole point - of bringing back a 3e-style magic item economy. "Rarity" isn't a charade, because it doesn't pretend to be a utility-based pricing formula. It's a pricing formula for games in which gold doesn't matter, and magic items make you just better (which is an understated, but factual, way of saying 'break the game').
5e's meant to be for fans of all past editions. That should (and does) include fans of the classic game who expect magic items to be powerful/exciting/interesting potentially character-defining/game-breaking and entirely under the DM's control. That should (and arguably doesn't) include fans of 3.x/PF who want wealth/level make/buy that lets everyone customize their magic item selection and lets casters burn exp for gold to do so, and thus provides lavish rewards for system mastery. And, yes, that even should (and doesn't) include fans of 4e who want wealth/level & make/buy of items that assumed into balanced scaling and even feasibly opt-out without disrupting that progression.
This is one of the areas where 5e has fallen short. You can't just slap on a pricing system to 5e's classically-designed items and get a 3.x/PF, let alone a 4e, functionality from them. You might get a nice call-back to an old Monty Haul campaign trying that.[/QUOTE]
I think only the most hard core of 3E fans think that the pricing things for 3E are actually a key feature of the game. Most 3E players (and PF players come to think of it) I have encountered are not the best at min/maxing which seems mostly confined to online discussion and perhaps OP.
IDK if the 4E players think that is a key feature of 4E either and there is not enough of them in any event (2% or so online tables).
If I had the choice of a reworked 4E or 3.x type game dumping the magic item Christmas tree and treadmill effect would actually improve both systems as the most appealing parts of those systems are not the way they deal with magic items and both of them could use AD&D magic items(under DM control) IMHO and probably improve the game.