Here's my suggestion. I'm something of a house rules minimalist so the idea of creating a wide variety of feats for crafting, or using skill challenges, doesn't sit well with me. In addition, I like to encapsulate my house rules into feats (they're easier to refer to on a character sheet).
Please let me know what you think. I just made this up so some of the time/value conversion might be way off. My goal was to have an open-ended skill list that allowed people to make mundane items and small sums of money in a very short time period, but was financially vastly inferior to killing monsters and taking their stuff.
BACKGROUND SKILL
Benefit: You are trained in two background skills. What qualifies as a background skill is ultimately up to the DM, but may include crafting skills (such as armorsmith, baker, boyer, carpenter, chandler, fletcher, haberdasher, leatherworker, tailor, weaponsmith), professional skills (such as accountant, bartender, clerk, farmer, horse trainer, lawyer, mercenary, merchant, sailor, scribe), knowledge about a particular area (no larger than a city or a region of the countryside), skills pertaining to social groups or status (such as noble etiquette, heraldry, military procedures, traditions of a particular tribe or ethnic group) or any other specialized form of knowledge that isn't well represented by normal skills, but isn't terribly useful during an adventure either. Your DM decides whether a background skill is appropriate to the campaign, and which ability score it uses as a key ability (typically, Intelligence or Wisdom).
You get a +2 bonus on any normal skill checks or ability checks related to one of your background skills. You can also make background skill checks:
Background Skill Check: 1d20 + 1/2 your level + the key ability of your background skill + 5 (if trained) + 3 (if focussed)
The DM sets the DC of the background skill check, and determines the effects of a successful check. In general, background skills let you know information relevant to your background, similar to a knowledge skill, and may be required to perform specialized tasks relating to your background. The DM may allow you to make an untrained background skill check for a background skill you don't have, which is the same as an ability check. However, the very nature of background skills means that many tasks associated with them require specific training and can't be attempted untrained.
If your background skill is one which can be used to make a profit, you can make skill checks to try to earn a living. Each week that you practice your craft, you can spend 10sp on raw materials, and then make a background skill check. You earn 1sp per point of your result (so if your result is less than 10, you actually lose money this week). If you want, you can instead spend 15gp on raw materials, and earn 1gp per point of your result (but you must make this decision before making your background skill check). Your trade may have additional requirements to be profitable -- for example, a merchant needs a market to buy and sell goods, and won't earn any money in an uninhabited wasteland. A sailor needs to spend some time sailing, etc. You can Take 10 on the check if you are earning sp, but not if you are earning gp -- high-stakes industries are a bit more volatile than everyday enterprises.
If you are crafting items, you can decide to keep the items instead of selling them on the open market. You need to state ahead of time what sort of item or items you are crafting, and the money you would have earned from background skill checks instead represents progress you are making on the item. When you've earned enough money through background skill checks to cover half the cost of the item, the item is completed. (Any excess money earned can be converted into more items or kept as money.) The DM can rule that certain items are more or less expensive to craft than their market price would indicate; for instance, the cost of crafting ritual components is equal to the cost of the components (not half price). You can't use background skill checks to create magic items, but you can create mundane items and then use the Enchant Magic Item ritual on them.
Example: Hrothbert the dwarf wants to create a magical suit of armor. He is level 13 and trained in Background Skill (Armorsmithing), which is based upon Strength (the DM decided that force of your arm and the quality of your training matters more than raw Intelligence when working armor), and has a Strength of 19. His total Background Skill (Armorsmithing) modifier is +15 (6 for 1/2 his level + 4 for his Strength + 5 for being trained). Hrothbert rents a forge and buys some iron, for a total cost of 15gp, and spends a week hammering away. He rolls an 8 on 1d20 for a total check result of 23. Since he is making platemail, which normally costs 50gp, he needs to score 25gp worth of check results to complete the armor. Hrothbert is 2gp shy (he's got a nearly full set of platemail -- it just needs a little more work on the ankle guards) so he spends another week, another 15gp, and rolls a 16, for a total result of 31gp worth of crafting. That's enough to finish the platemail and produce another 29gp worth of armor -- so he decides to make 29gp worth of guantlets and sells them immediately, pocketing 29gp of profits (these sales are part of the normal activity of being an armorsmith and doesn't take up any extra time or energy). Hrothbert has spent a total of 1gp (29gp worth of profits, minus 15gp weekly expenses x 2 weeks) to produce his platemail. Finally, since Hrothbert has the Ritual Caster feat and knows the Enchant Magic Item ritual, he goes out and buys 17,000gp worth of alchemical reagents. He then spends an hour performing Enchant Magic Item on the platemail, turning it into
+3 mountain platemail, a level 13 item and dwarven specialty.
Special: All characters start with this feat at 1st level. You can use the normal retraining rules to change which two background skills you know. By spending feat slots, you can select this feat multiple times, adding two new background skills each time. You can select "Skill Focus (Background Skills)" as a feat, in which case the +3 bonus from Skill Focus applies to all your background skills.