Know of something you feel would improve this addon? Feel free to leave a comment detailing it the best you can and I'll see what I can do.
BuyEmAll
Created and maintained by Cogwheel to v2.8.4. Now maintained by Shinisuryu.
BuyEmAll enhances the shift-click interface at vendors.
Features
Type in the amount you want to buy
This is actually part of the default UI. Enough people don’t know about it due to the fact that there is no cursor and clicking in the box gives no feedback, that I decided to list it here.
Buy more than the stack size of the item at once
For instance, if you want to buy 80 pieces of Silk Thread, you currently have to shift-click the thread, enter 20, hit Okay, shift-click the thread, enter 20, hit Okay, shift-click the thread, enter 20, hit Okay, shift-click the thread, enter 20, and hit Okay.
With BuyEmAll, you shift-click the thread, enter 80, hit Okay, and confirm that you want to buy more than a stack. This confirmation appears so you don’t accidentally buy 1000 of something when you meant to buy 100.
Shift-click items that come in preset stacks
The default UI doesn’t allow you to shift-click items like Refreshing Spring Water which come in preset stacks. If you want to buy 50 of them, you have to right-click the item 10 times. BuyEmAll allows you to shift-click the item and enter the amount you want. See Notes for more information on preset stacks.
Know how much you will be spending
Below the box where you enter the amount is a money display. This updates as you change the amount you are going to buy, showing you exactly how much your purchase will cost.
Quickly fill stacks or buy as much as you can
The BuyEmAll window has Stack and Max buttons which allow you to enter a full stack or as much as you can afford/fit. Hovering over the buttons shows a tooltip with the number of items you will be buying and how much it will cost. See Notes for information on the maximum you can buy.
If you already have some of an item, the first click of the Stack button will enter the amount you need to fill that stack. Subsequent clicks will add full stacks to your pruchase.
Quickly refill your ammo pouch
If you are buying ammo and have free spots in your ammo pouch/quiver, the amount that appears when you first shift-click the ammo will be however many stacks it takes to refill your bag. Just hit Enter/Return, and you bag will be filled.
Notes
Maximum Purchase
The amount you can enter is limited by:
The amount of free space in your bags. Partial stacks are included in this calculation, as are specialty bags (e.g. free slots in enchanting bags will be only be counted towards your free space if you are buying an essence, dust, or shard).
The amount you can afford.
The amount available from the vendor (for limited stock items).
A breakdown of these numbers is included in the Max button’s tooltip.
If you can only buy one item for any of these reasons, shift-click behaves just like a left click, picking up one of the item onto your cursor. If you can’t buy any, then shift-click does nothing.
Preset Stacks
When you are choosing the amount for items that come prestacked, the amount you enter is the total amount you want to buy, not the number of stacks you want to buy. If you use the arrow buttons, this number will increase or decrease to multiples of the preset stack size.
The confirmation window will only show up if you buy more than the maximum stack size in your inventory, not the stack size that you can buy at once.
Example
Refreshing Spring Water — Stack Size: 20, Preset Stack: 5
If you enter 18 and hit Okay, it will automatically buy 20 with no confirmation. If you enter 23, a confirmation will pop up asking, “Are you sure you want to buy 25 of this item?”
Currently, the Stack button is overzealous about items that come in preset stacks. If you have 3 Refreshing Spring Waters in your inventory, clicking the Stack button will enter 17 as the amount, and you will end up purchasing 20. Future versions will handle those situations more gracefully.
Bugs
None to my knowledge. If you find any, please report them!
Change Log - BuyEmAll
v2.8.7
No reported issues, TOC bump.
v2.8.6
Replaced the rewritten code with an edited version of Cog's original space calculation code, works as it did in 2.8.4, with better support for profession bags/items.
v2.8.5
Rewrote bag space calculation.
v2.8.4
Fixed bug with confirmation dialog.
v2.8.3
Added more localizations for zhCN and zhTW, thanks to q09q09
v2.8.2
Updated for 3.0.2.
v2.8.1
Updated for WotLK Beta.
v2.8
Cost of Stack or Max purchase now shown in the button’s tooltip instead of changing the money display.
No longer displays “loaded” message.
Separated localization files for more flexibility.
But I was unable to do shift+left-click link in chat from the tier 9 vendors. BuyEmAll would show instead of pasting link like it does when you shift+right click other items.
But I was unable to do shift+left-click link in chat from the tier 9 vendors. BuyEmAll would show instead of pasting link like it does when you shift+right click other items.
Originally posted by sevvie Awesome Never considered an addon like this... but I certainly know I hate buying 100 different stacks of arrows. So I think me and this addon will be close friends
Awesome Never considered an addon like this... but I certainly know I hate buying 100 different stacks of arrows. So I think me and this addon will be close friends
Originally posted by ForeverTheGM Maybe you could add a check to see if GnomishVendorShrinker is loaded and if it is, replace its stack-split window with BuyEmAll's?
Well, unless there's something I don't know, which is very possible, but unless I can somehow replace a function in GVS, I don't think I can make BuyEmAll work. I'm still looking for other ways however.
Alright, I *think* I got it working like it did before, I totally forgot that I didn't take into account partial stacks. Sorry for taking so long, should have the new version up later today, once I've gotten some sleep and done a few more tests.
Never considered an addon like this... but I certainly know I hate buying 100 different stacks of arrows. So I think me and this addon will be close friends 
