Sims 3 Economics
In the first Sims game, it was hard to make money. I remember sending my Sims to work, day after day, saving up to buy the best hot tub. Remodels also required many Sim days - sometimes weeks - of saving in order to finance. For Sims 2, Maxis changed the economics so that it became ridiculously easy to accumulate vast amounts of Sim wealth.
EA has swung back the other way with Sims 3, making it far more difficult to accumulate wealth. I find that the biggest cash suck is the skills system, which you have to pay to climb. In previous games your Sims purchased a bookcase, and whenever they wanted to level up, they would just sit down and read that one cookbook that came with the bookcase. Now you have to buy books separately, one for each skill level, and the books are pricey!
Just as an example, the Level 1 skill books (cookbook, mechanical, charisma, etc) cost 50 Simoleons. The level 2 skill books cost a whopping §500. To put these prices in context, I have a Sim who is level 3 on the Medical career track. She brings home 179 Simoleons per day. She has to pay the babysitter 75 Simoleons per day to watch her daughter while she's at work. Not counting any other expenses (and there are tons), it would take her five work days (an entire work week) to be able to afford the Level 2 cookbook.
Fortunately, there are some ways around these prices. For one thing, Sims seem to learn skills faster by practicing them than in previous days. My Sim reached cooking level 3 almost by accident, simply by preparing meals every day for a few Sim weeks. And once you accumulate 10,000 Lifetime Rewards points, you can purchase options which make things cheaper. I had one Sim purchase the "Bookshop Bargainer" Lifetime Reward, which puts the level 2 skill books at 380 Simoleons each. That's a major savings!
Unfortunately, even though you can buy books and store them in the bookcase, each skill book disappears once your Sim has read it. Apparently the skill books are a consumable item, which is pretty bizarre if you think about it. (This only applies to the skill books, by the way - the other books can be read, re-read, and read by multiple Sims.) (Corrected information can be found in the next post.)
Specifically with regards to the cooking skill, there is also a separate set of single-recipe books. Your Sim may have read all of the cooking skill books, but if she wants to learn how to make Ratatouille or Fruit Parfait, she is going to have to shell out for those specific books - 25 Simoleons apiece. And once again, the books disappear after she reads them. So she can't re-shelve the Ratatouille recipe so that her daughter can read it when she grows up. Other recipes cost even more, I think the fanciest recipe (lobster thermidor, if I remember correctly) costs 500 Simoleons .
Clearly the best strategy is for each generation of a family to have one Bookstore Bargainer whose job is to buy all of the books. Saving 120 Simoleons - almost an entire day's wage - on a second level skill book is going to give your family a major advantage!