Hey Tall. If you want to use command blocks, be my guest, but if you want strictly redstone, try this out here: http://www.youtube.com/watch?v=f20-7iCW1M8.
All you need to do is add an item sorter that sorts the items into a chest using a this video here: http://www.youtube.com/watch?v=IdDABs7v-4Q.
Use your preferred means to check if the chest is filled with 5 items, then replace the button in the first tutorial with a pulse, after setting it for the amount of items you would like to dispense.

Hope this helps,
-Sanctum

now this is iffy, as too much iron could cause you to lose it all. i suggest giving a 1 stack for any amount trade rate if you use my method. it will prevent the player from losing iron accidentally

use /testfor to test with a chest with 5 iron ingots (has to be slot specific), and replaces it with a bread chest. then, when the chest is empty, more iron can be put inside. i would imagine that this is what foxsong is doing.

I have an idea about how to make a repeatable one
I'll post a download link after I get finished building

EDIT: well it seems as though several people have beaten me to it X)

Yes you can however you can only do it once as far as I know.
-The way you do it is to have two hoppers on top of each other (top hopper must be connected to bottom) then have a comparator put in front of the bottom hopper.
-Next you need to put a redstone torch to the side of the comparator. Finally just put a command block to the front of the comparator with the command /give @p 297 64
That's it for the construction.

The most important part is to put 59 ingots of iron into the hopper. And then fill up the rest of the hopper with items that don't stack like water bottles, or swords.

I realize this may be hard to build the way I worded it but Im certain there is videos out there.