I've been percolating on this idea for awhile now, but I wanted to go ahead and share my experiences. A couple of months ago I bought the recipe for Moonshadow Armguards on the Auction House. Someone had posted it for like 500g (I don't remember exactly what I paid, but it was cheap). I was wearing the 213 badge bracers at the time, so these crafted ones would be a pretty good upgrade for me. At the time I thought that was a worthwhile price for an item I could make myself and get a BiS level piece of gear. For a few weeks I picked up low-priced mats on the AH and set them aside for the bracers. Then I got sucked into a ToC25 run with another guild and scored the Bracers of the Autumn Willow. At first I was excited to get an upgrade, then annoyed. The drop bracers were very similar to the crafted ones and now there was no need for me to make them.
Meanwhile I still had half the mats in my bank and a new recipe I'd paid for and not used. After a brief period of mourning (I love wearing my own goodies!) I decided to finish the project and make the bracers to sell. This was right before 3.3 dropped. Since then, I've made several crafted items from UD25 and ToC recipes and they have all sold for good money. It seems people are willing to pay several thousand gold for an item that gets them close to 3.3 raid status.
If this sounds like the kind of thing you'd want to try, I would first encourage you to start looking for good recipes. Use your personal experience on gearing to guide you on quality pieces. For example I know that the Indestructible Plate Girdle is the best tanking belt you can get without raiding or spending Frost Emblems. Oddly enough, my Smithing alt picked that recipe up a few months back. Like the bracers, I've sold several of the belts for a 50-100% mark-up over the cost of the mats. So keep your eyes on the Auction and try to pick up one of these recipes for a good price. I would say anything in the neighborhood of 500g is a great price. Don't be afraid to bid on an item that's opening bid is notably lower than the buyout and see if you get lucky. Spending 500-1000g is workable if you're confident you can sell more than one of the item. You should be able to make at least 500g per piece you sell. You have the potential to make 1000g or more on these items if you keep an eye out for bargain mats and use profession shortcuts to your advantage.
A significant professional shortcut is open to Leatherworkers. I made over 1000g on each pair of bracers I sold by purchasing all leather mats with Borean Leather and converting up. It's not too difficult to get regular borean leather for 10g a stack if you jump on auction gluts. Three stacks of regular leather convert into ten heavy borean leather for 30g. Normally you'll pay 5-10g apiece for heavy borean leather on the AH, so already you're saving at least 40% on the cost of leather. In addition, you can convert 10 heavy leathers into an Arctic Fur via the leather trader in Dalaran. If you do any AH shopping for Arctic Fur, you already know that no one ever sells their Arctic Fur for 30g. The lowest I've seen in my casual shopping is about 50g and it can go up to 100g on a bad day. So once again, we're saving 40-60% on the cost of leather goods by converting. All you need to do at this point is pick up the necessary orbs/eternals and you're good to go.
For Blacksmithing the professional shortcuts aren't quite as amazing but you can take advantage of an Alchemist alt/buddy to help you out a bit. If titanium is selling for more than the cost of 8x Saronite Bars/16x ore, buy the Saronite! An Alchemist can convert these bars to titanium with no cooldown, so they can crank out as many as you need. The saronite conversion is even better if your Alchie is specialized in Transmutation - you get procs! I've proc'd as many as 5 bars on a transmute :) Transmutation is the main reason titanium prices are dropping, but there are still fluctuations that could result in you paying too much. It's also more important for you Smiths to keep an eye out for bargain eternals since they influence your titansteel costs. There's a lot of fluctuation in shadow/earth/fire depending on how many sellers are posting. Make sure you get in on the deals, you can save 30-50% off the price by shopping smart. When you finally do post your crafted item for sale, price it based on the titansteel bars, not what you paid for the titansteel mats.
Unfortunately I have no professional tips for Tailors since I'm still leveling mine. I'm sure a strong benefit is the specialty cloth proc, which let's you make your cloth for half price. If there are Tailors out there with UD/ToC recipes that want to share their experiences, feel free to leave details in the comments :)
Once your item is done, I either price it comparable to the other sellers or I sell it for the "retail" value of the mats. There's not a ton of competition at this level, so it's unlikely you'll have more than one or two other sellers with the same item. It's unusual to see someone selling these "high end" items for cutthroat prices, but if you happen to run into that just wait a day or two and try again. One thing I've noticed is that the chest pieces tend to sell for lower profit margins than the lesser pieces. Considering the mats are generally double on the chest gear, selling prices are not reflecting that difference. For this reason you may not want to deal with chest gear unless the price is amazing (or free aka looted) or you are really sure you can still make a good profit.
I suspect that some of you, like me, have been leery of getting in on the crafting action for 226+ goodies. However, I lucked into a few recipes and I've had pretty good experiences with them. That's why I'm posting now, to encourage those of you who've been considering moving into this area. I wouldn't spend more than 1k for a recipe, but some recipes are selling in the 400-600 range since 3.3 dropped. This may be a good time for crafters to jump in and take advantage of the market for pre-Icecrown gear while the players are still willing to pay good prices for it.
Feel free to share your experiences with selling these items in the comments!