Levelling crafting on the cheap

If we look at what the 'average mug' crafter does, we can 'structure' our training to take advantage of this, both as a crafter and as a gatherer
Dont be these guys:

• Would like to learn a profession.  Spends a fortune on stuff in the AH. Doesn't finish in twenty minutes and gets bored. Gives up.
  
• Knows that some professions go together - like herbalism and alchemy.  Tries to keep up, but cant be bothered.  Finds that they get to level 40, and can't gather anymore.   Gives up.
• Can't get into their raiding guild without a profession.  Takes 6000+ to AH.  Cant find all the mats in the AH. Spams trade and pays 3 times going price.  Uses a profession levelling guide. Sells everything at a vendor.  Runs out of money.  Begs for gold.  Might even get profession, but will never make money from it.

The 'simple' way to level your crafting professions will, by my rough and ready numbers,  set you back about 6000 gold.  However, as much as possible - I have a break even (or better) policy.
Stating the bleeding obvious (I do that sometimes), once you have the recipee, your profit or loss per item is [sale price of final product] - [cost of mats]. The total cost of levelling = Training cost + sum of (profit or loss per item) + time.

In WOW, the cost of recipees is trivial compared to the cost of mats.  For flexibility, I learn everything the trainer has to teach me.  I also keep an eye on what other vendor recipees are available.  You can find recipees while 'doing other stuff' (I always buy a few when I find a new vendor with a recipee), on the AH, on a web professions list like thottbot (toggle the 'menu'), crafter's tome, or an addon like Ackis recipee list.

Getting skill points
Each time you craft something, you have a chance to level your skill, based on its difficulty.

• Red: Cant learn this yet.
  
• Orange: Will level.
• Yellow: Usually level.
• Green: Sometimes level.
• Grey: What's a level?
  

Costs:
If you are levelling a related gathering skill (say herbalism for alchemy), because you either like the buff (lifebloom), or are considering gathering as a career option, you will have an easier time learning your tradeskill.  Regardless of whether you are levelling via your own gathering or the gathering of others, the Auction house can be your friend.  Regularly look at what you need both now, and what you need later, and if its cheap buy it.  If you have surplus mats sell them. Also for many professions you can make 'parts' at a lower level and use them at a higher level.

Sale Price
While you are levelling your crafting profession, you are going to have a lot of items to get rid of.  Vendors will pay you a pittance.  Some auction house items sell for well over their cost of mats, some for the same pittance as your vendor.  As a rule of thumb - if a "fail" crafter from above can sell it - it will sell for nearly vendor cost.  Item's for 'Twink' (generally PVP), unrelated trade skill (i.e a blacksmith item needed for leatherworking), rare items, vanity items, quest items (eg hillmans cloak), and wands (for enchanters) it will sell for more - often at a profit.
An easy way to tell what sells 'well' on the auction house is to use auctioneer (or from curse / wow interface) or a similar addon and do periodic scans of the aucton house.  If you are planning on selling via the auction house, try to varied items, get your bank alt lots of bags and trickle feed the items on the auction house.
Surplus Common ('White') items from early levels may be betst sold at a vendor.  Uncommon ('Green') items or better can generally be disenchanted.  Enchanting mats usually sell well (make an enchanter or friend - or maybe even make your friend into an enchanter).

Profit or loss per item
Continuously working out what items are going to make a profit, small loss, or very large loss can be ... difficult.  Lil Sparky's Workshop shows you the market value of both the mats to craft an item and it's final sale price.

In summary

• Consider additional recipees.
• Look for mats for both tomorrow and today.
• Keep an eye on both cost and sale price.  Consider disenchanting surplus items.
• Addons I use : Auctioneer, Lil Sparky Workshop, Ackis Recipee List.