I got tired of doing all the math in my head to see how much money I was making off crafting bags with Tailoring. Pretty simple spreadsheet. The profit does not include the AH posting fee because sometimes stuff doesn't sell the first time you post it, but it does include the 5% AH cut. I didn't look around for the forums to see if something like this was already out there, so don't spam me and say "already posted" if there is one. The Illusionary Bags can be made cheaper using your weekly cooldowns, but I didn't include them.
Bags that are included: Netherweave, Embersilk, Frostweave Bag, Hyjal Expedition Bag, and Illusionary Bags.
All you have to do for this spreadsheet to work is enter the AH prices for the materials for the bag you are crafting, the spreadsheet will do the rest of the work.
Link/Download.
Code:
https://docs.google.com/spreadsheet/ccc?key=0AgT94bLw3S3-dFUxY2tTR1dIUkhPSEF4ZmlVd0Y2WlE#gid=0
After you open the spreadsheet make sure you click file > Make a copy, or you can download it.
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
-~-Step by Step guide on how to use this spreadsheet.-~-
For this example I'm going to use Frostweave bags. The spreadsheet shows the raw materials needed to make a bag. In the spreadsheet, I provided links to wowhead for each bag and it will tell you have you have to turn the raw mats into.
1. Figure out what bag you wanna make and look up each item on the AH and check the price. For a Frostweave bag, you will need Frostweave Cloth, Infinite Dust, and Eternium(Buy it from a Tailoring Vendor). You also need to get the price of a Frostweave Bag.
2. After you find the buyout price per item, you will need to enter them into the spreadsheet. The only column you will need to edit is the "AH Price for One" column.
It will look like this at first

After you enter all the prices, it will look like this.
3. So now that you have entered all the prices, you can now see if it's profitable to buy the mats and craft the bags to sell them at auction. Currently with these prices on my server, I would lose ~51.49g if I was to buy the mats to make the bag, and then sell the bag on the AH.
The blue background cell is the cost of the bag on the AH.
The teal background cell is the cost of a bag if you bought the mats and crafted it.
The green background cell is the amount of gold you would make/lose if you crafted the bag and selling it after buying all the mats. This number is the amount of profit/loss you will make after the 5% auction house cut.