Non-general store merchants now carry nearly no gold. The only viable way to sell things to them is to buy things first, similar to a “barter” system like Fallout 4, although limited to Skyrim’s engine. General store merchants also carry less gold. I found it unimmersive that I could “force” NPCs to buy my limitless quantities of crap and it led to getting too much money too quickly. Now if you want to sell things for real profit and not just as collateral in trades, you will need to either invest in their shops or find a fence with much more gold. Selling goods doesn’t make too much money unless you decide to invest in speechcraft.
In exchange, quest rewards and loot give more gold so that you are encouraged to take on objectives. You can make a living and earn enough gold just by exploring and clearing locations.
Peerless enchantments can be found at fixed vendors across all of Skyrim and Raven Rock so that you don't have to repeatedly abuse Endarie and quickload to get the enchantment you want. They are sold at a higher cost than naturally found ones.
In general, items that you want to purchase are now more readily available from the proper vendor.
Enchanted arrows and bolts
Skooma
Rarer alchemy ingredients
Enchanted varieties of armors and weapons
Scrolls (especially knock scrolls)
Various beneficial potions
Meals (food)
Master keys
Many items have had their prices adjusted to incentivize buying them more often
Various potions and poisons
Scrolls
Spell tomes
Carriage rides, houses, plots of land, rooms at inns, and trolls from Dawnguard have their prices increased. The house in Windhelm might appear cheaper than others, but you're a war hero after all