I am day 2k and 1 unit of grain is well 30 denars now in some towns. Is this because of denar inflation or super high demand? Grain producing villages being raided too much maybe?
Possibly unrelated consequence but I've noticed starvation seem to be a much more significant issue for armies now. -- are these related?
Anyone else seeing similar effects in the economy in the later game?
It is both inflation and increased demand.
The way it
generally plays out is that continent-wide prosperity rises continuously. Prosperity is a huge drain on the continent's grain supply, especially at higher levels like 8000+ and the grain supply (from grain villages) can only keep up to a certain point. That certain point is every grain village near to the town at above 600 hearths, so they produce 150% their normal daily amount of grain. Villages under 300 hearths (IIRC, not looking through game files right this moment) only produce 50% and obviously raided villages produce nothing.
Additionally, prosperity at a high enough level (I forget when it kicks in, but it might be 6000? don't quote me on that though) produces an inflationary effect in the town, at least as far as trade goods are concerned. That ties back into the grain consumption because towns with very low prosperity have cheap goods which caravans snatch up and take to high prosperity towns.
Another massive and overlooked consumer of grain are lord's parties. They have the same supply needs as player's party and will gleefully strip every scrap of food from a town to support their troops. That isn't much of a problem at the game start, but AI clans gain tiers just like the player's clan and in a twenty year playthrough most (if not all) will be at tier 6. That means much bigger parties (160-200+). Also, influence accumulates for AI clans as well, which means much bigger armies (1800-2400 are totally normal sizes) with massive, massive supply needs due to their slow speed. They have no problem buying every foodstuff in a town just to reach the next town and repeat the process, until disbanding and being instantly reformed again (maybe under a different leader) to continue the cycle.
Taken together with increasing prosperity and inflation, grain prices are naturally driven higher. How much higher depends on a playthrough; I had one where there were a handful of mega-cities (over 10,000 prosperity + 500 men in garrison) that ate so much grain just from their daily needs, every other settlement was in various degrees of starvation. Grain was quite expensive (I think anything under 20 was a good deal) and any town that produced serious amounts of it would have it plundered by caravans to be hauled off to the mega-cities for huge profit. Other playthroughs weren't nearly as extreme because there have been changes to the game's economy since then to help stall prosperity growth, due to its quite literally gamebreaking nature.
But you have to expect price inflation for food, even without mega-cities, in a long playthrough. There are going to be more and bigger parties roaming the map, along with prosperity rising.
On the plus side: it makes affording your party easier over time because troop wages are fixed while potential income from trading, fief ownership and workshops steadily ticks upward.
All this comes with a caveat that it is personal experience, virtually all of which has been pre-pillage mechanic. Pillaging definitely has had an economic effect on my game (partially due to an early oversight) but I don't have multiple playthroughs to say anything solid about how bad it should be or usually is.