Dark Sun Setting has always been one with little real wealth. Life is a struggle due to the harsh environment made all the worse by a lack of resources. The lack of metal was previous played out by either using a select number of weapons what did not require metal or using weapons whose metal components were replaced with various other materials. These other materials would affect not only the weapons ability to hit and the damage it could do (negative modifiers) but also had a chance of breaking with use. But since metal armor was also rare the armor classes of targets were also limited where the toughest commonly encountered armor was Hide.
In the new edition while metal is still rare, they have done away with the modifiers and the breakage while still there is total different. While in a certain way this makes sense, nonmetal armor does not protect as well so the nonmetal weapons perform as expected, they really do not have an advantages for using a metal weapon. Sure it might break a quarter as often in use but these are supposed to be great treasures. Probably metal weapons used on non metal armor should pick up an extra nonmagical enhancement bonus. Sort of makes them like lower level magic items.
The old rules used to have a piece mail armor system since a single steel breatplate could gave you better protection than most hide armors but that is also gone leaving only a rule about where a full suit of metal armor in the sun is going to be very hot. I think a full suit of hide armor would also have the same problem.
Dark Sun is also not supposed to be a world litter with magical items so the new rules have some options for this. First they have a fixed enhancement bonus system which improves characters attacks and defense as they go up in levels at a rate slightly slower than they would get with magic items. This allows the characters to still handle challenges of the proper level without everyone having to be loaded down with magic items like you are playing some MMO game. This is a great idea. To keep magic items lower they talk about removing and replacing treasure bundles. I have not taken a good look at the DMG so I cannot really comment on this.
Dark Sun is not really a place where you should be able to buy magic items. You might be able to sell them to some major players at the 20% value discussed in the players handbook buying them at any value should be very hard.
Item Value and Coinage has always been different on Dark Sun. Formerly anything not made of metal was considered 1/100 th the cost and copper pieces were replaced with ceramic pieces. So anything that used to cost 1 gp was now 1 ceramic piece and things that cost a silver piece cost a bit (1/10 th of a ceramic piece). This lead to some problems in that things also cost copper pieces and now you have no value small enough for that. This flat change also had some problems in that some things made of metal like the classic iron pot cost about 5 sp but had a material cost of the like 2 gp in metal. With laborers making less than a bit per day, a metal longsword at 15 gp represented a fortune.
In the revision they got rid of the funny down scaling of the currency but did not but a specific new value on metal objects. They say that city states produce ceramic coins of different values backed by their governments(like a 1 sp or 1 gp face value ceramic coin) and various trader with exchange these for other city states coinage at some discounted rate or exchange metal coins at full value to ceramic. This part is just not right. I like the idea of the different denominations of ceramic coins each back by the different city states. This gives a lot of flexibility and uncertainty in the value of things since Tyr currency is probably not valued very high currently in other city states. But saying that all the City States keep there currency on a gold standard does not make sense in this world. If a character starts out with 150 gp worth of equipment than that is the equivalent of 3 pounds of gold if anyone would actually do that exchange for you, but no one will so gold must really be worth a lot more. Using the Classic Scaling you get that gold is worth 5000 ceramic gold pieces per pound, 500 for silver, 50 for copper, and 100 for iron. Metal object probably cost about their weight times 2 for simple objects and 4+ for complicated things. It will be up to the GM to decide and find ways to keep even higher level characters from amassing to much wealth.