The big changes in the economy are in two areas, magic items and armor. The rest of the economy is largely unchanged.
In 4th editions magic items were not only a key part of the economy they were a super important part of making the math work across the system (particularly in the areas of to-hit, damage and defenses). If you didn't have on level or so magic equipment, you weren't effective.
5e is built to be different in this way, it is expected that in most campaigns magic items will be rare and the math is built in such a way as to make them optional, and powerful when available.
In 4e magic item purchase and sale was handled two different ways over the life of the edition. Originally there was no limits on what could be purchased when beyond what the DM ordained. Later in the edition all magic items were given a rarity value (common/uncommon/rare) and it was ruled that only common items were available for purchase and that uncommon and rare items could only be found. Items of any rarity could be sold though (and at a rate dependent on their rarity).
In 5e magic items are not generally available for sale and are so far never listed with prices, though rarity is still very much a thing (though I hesitate to enumerate the list until we get the DMG as I'm not sure my enumeration would be complete.).
However, we can take a look at the overall economy by getting a flavor for the mundane price differences. Let's take a look at a longsword, a shield and a day's rations in each edition:
weapon 4e price 5e price
longsword: 15gp 15gp
shield 5-10gp 10gp
rations 5gp/10days 5sp/1
From this randomish selection of items, it looks like the economy is expected to be about the same with regard to mundane items. I haven't done an item by item comparison, but the only big differences is that armor prices increase to prevent low level characters from having things like full plate at L1.
Presumably wealth by level or some similar mechanic for awarding treasure in general will be presented in the DMG, but for now, since treasure has very little impact on the game (it impacts cost of living and armor quality, but not much else), it should not be a problem to simply convert an old adventure verbatim on cash.