The DMG, Section by Section, Part 10: Money

Player Character Starting Money

Gary doesn't actually spell out how much money characters get during character generation; I assume both that that's in the PHB and that the amount of money characters get is 3d6 x 10 gp. Gary stresses that it is important for characters not to have everything that their players want them to have, for the characters to always need more (at least to keep up their lifestyle; Gary points out that the assumption is that adventurers [except for monks, so apparently including paladins and rangers] are living the high life whenever they aren't risking their lives in the dungeon). Gary argues that this is the way to make sure that players are still interested in adventuring. From what I've heard, that might be necessary for some players of the "YOU-give-my-character-his-motivation" school; I've had the good fortune of never having players who don't provide their own characters with motivation. Actually, most of my players who thought about any motivation past "exploring, fighting and getting rich" found the idea of the Old School endgame very compelling.

I realize that's not every player, though, and this is an easy way to give a PC motivation (here's another).

Also, it can't be denied that there's a certain pulpy romance to the PCs constantly making do with less than they want and constantly going into dungeons to get the gold to acquire it. I prefer justifying PCs being less wealthy than they'd like because, well, that's what this game is about rather than because the player's won't play if I don't adversarially inflict poverty upon them.

Player Character Expenses

Characters spend 100 gp per level per month for room, board, equipment maintenance and entertainment. I like this a lot, as it's incredibly simple; I'm not sure I'll use that exact amount, but this is definitely going into my game (my players tend not to be interested in living the high life quite as much as Gary expects). Characters also have to pay henchmen 100 gp per level per month, in addition to their standard treasure shares. Once they have a stronghold, they also need to pay 1% of the total cost of their stronghold per month. Gary also suggests taxes, fees and levies, but he leaves those to the discretion of the DM.

Gems

Gary provides tables for determining what and how valuable gems are. The basic mechanic is to roll on one table, which provides a base value ranging from 10 gp to 5000 gp. Rolling on the next table, that base value is adjusted to its final value. Finally, a roll is made on the appropriate table corresponding to original base value to determine what the gem actually is.

At least I think that's how it works. Gary is less clear than usual in this section, and the fact that most of the "what gem is this" tables have 13 or 14 items makes me wonder whether Gary wanted me to roll on them or not.

Reputed Magical Properties of Gems

Here, Gary gives a long list of gems with the magical properties they are supposed to possess, according to the general culture in the game setting. Which is pretty cool. He then points out that these properties are only what NPCs say these gems have. In actual gameplay, Gary is emphatic that merely possessing, say, a chrysolite, won't ward off spells. Which makes a lot of sense to me, since I don't want my players' first level characters running around with a pocketful of 10 gp gems they found in their first dungeon crawl getting to be invisible and controlling weather and being immune to magic, fire, venom and plague!

Gary does allow for the reputed magical properties to actually be true when gems are incorporated into some magic item, like a potion or ink (or a non-expendable magic item, I say; to craft a ring of invisibility, you should have to have a chrysoprase to set into it). That makes his list a lot like the components list from the Ready Ref sheets, except that it's a lot less dangerous to buy an amethyst than to acquire, say, a displacer beast's tentacle.

Values of Other Rare Commodities

Gary spends maybe a quarter of a column on the prices of other stuff you might find in a treasure hoard, like silk, tapestries, rich furs and spices. That's actually pretty helpful, as I don't recall most other RPGs having prices for those.