Most of us raid, and raiding is fun. End game content, seeing 9/24 other people coordinate to achieve the same goal, and finally taking down the boss and getting all the phat lewtz is a good time. I recently just joined the top raiding guild on my server, and it's a fun but intense experience; there's a lot of pressure to perform and a lot of pressure to put out good numbers. There's a few ways to do this: food, flasks, and pots. These are expensive, but let's talk about ways to keep the repair costs down.
First, you should be buying the mats and getting the items made/making them yourself. I guarantee that there is a flask-specc'd Alchemist in your raid if you're raiding 25 mans. If not, be sure to get someone to make them (preferably from your guild, that way you avoid the tip as well - this isn't rude, as I craft anything for guild-mates without a tip) beforehand. If you're making potions, be sure the person is a potion-specc'd Alchemist. For food, there's not much you can do.
I'd stay away from farming the material: if you're looking at it from a pure gold per hour standpoint, it's almost always "cheaper" to purchase from the Auction House. I know Deep Sea Sagefish (to make Severed Sagefish Heads) cost approximately half of the finished product. Pro Tip: You can also make these and sell for a decent amount of gold!
If you must buy pre-made flasks/pots, buy ONLY WHAT YOU NEED. Prices WILL come down soon, and you don't want to be the guy who invests 4,000g in flasks only to find out that the price dropped to half that in a month.
And of course, try not to die.