Well ships don't have costs either, and most Sci fi stories worry about life support when it's damaged. There are no costs, and you seem to be right about it being thematic.
They seem to be going for a more science fantasy setting, so it's not too surprising. In both Star Trek and Star Wars, being concerned about losing life support or running out of fuel is an infrequent story element. We always joked that the ship only loses its atmosphere if the "Plot Development" light is flashing...
That having been said, there is an easy opportunity to implement at least one of them: In starship combat, one of the critical effects is titled "Life Support". It would be easy to apply a small penalty to crew actions due to lack of oxygen, pressure or gravity if not having them would impair the character's ability in some way.
I am using a super quick house rule for Fuel. I just use the total PCUs as days worth of fuel. As the players have a small light freighter I've not written anything for increasing size of ship though.
You can extend the fuel storage with Expantion bays dedicated to said purpose too.
As for food and water on board, I use the quality of the crew quarters as a base. Lower quality quarters = less food and water. Once again, Expantion bays increase this.
No, there are not prices for maintenance or fuel or life support.
That's because money is not a resource in 3.X style games. It's a pacing mechanic, tied directly to XP, with some assumptions of the baseline math of the game coming from your experience progression, and some coming from your monetary progression, in was such that if one gets too far from the other, the math of the game breaks down, preventing the meaningful existence of an economy and forbidding money-making methods that deviate you meaningfully from your appropriate WBL. This is an inherent design flaw of 3.X style games.
So, even if there were a number on price of these things, it would, by necessity, be a trivial number that doesn't really matter and only means more accounting.
Besides, the game doesn't have to simulate every little detail. That level of accounting isn't fun. And it isn't unaccounted for; it just comes from a more abstracted asset pool. 3.X is not generic. Certain challenges aren't appropriate and aren't meant to be something the players face in a meaningful way or for a meaningful length of time. This is still heroic fantasy sensibilities; the system isn't set up to address the question of, "Can I make rent this month?" as a meaningful challenge past level 1. These basic resources are an occasional plot device, not an actual expense.
That having been said, there is an easy opportunity to implement at least one of them: In starship combat, one of the critical effects is titled "Life Support". It would be easy to apply a small penalty to crew actions due to lack of oxygen, pressure or gravity if not having them would impair the character's ability in some way.
Oh, God, in FTL, I was absolutely evil about that. One of my go-to strategies was to have a bunch of ion cannons, then cycle through shutting down systems such that weapons, shields, engines, and life support were always down, until everyone suffocated and I got the boosted salvage value for an intact ship.