Yesterday, Roll20 emailed publishers the news that print-on-demand prices would increase. I saw the news hit BlueSky and other social media platforms shortly afterwards.
Publishers were warned to ensure they had enough margin in their own prices, gamers were urged to buy before April and beat the hike, and the brewing trade wars were (rightly) blamed.

There’s been an error. Prices are increasing more than first announced, except for high-end US colour. Today, Roll20 had to issue an error correction.
Sites hit by the hike include but are not limited to DriveThruRPG, DMsGuild, Pathfinder Infinite and the Storytellers Vault.
The country being hit the hardest is the US, where print-on-demand black-and-white books will go up by 20% for small books and 50% for large ones. Colour printing will increase by about 12 to 13%. The cost of premium colour books in the USA will drop slightly.
In the UK, the price rises are more modest with black and white going up by between 3% and 4% while, colour by about 3% and premium colour up by a bit.
Roll20 shared a pricing adjustment table with publishers. Please note, these are material costs and not what gamers pay for when they buy the game, which also has to include art costs, layout costs, writing, license fees and a host more.

Photograph by Volodymyr Hryshchenko.