-A rather large green shirt (I used a women's XL t-shirt - $5 at a thrift store)
-White Undershirt (Already owned this from a previous costume)
-Brown Tights ($3)
-Brown Boots ($8, thrift store)
Foam Board for the shield ($2, Walmart)
Brown Scarf ($2, thrift store)
Brown belt (already owned)
Plastic sword (or make your own with spare foam board!)
Blonde wig (unless you're already blonde!)
Green Fabric ($3/yd - walmart)
Various colored paints
The main costume is the easiest part! Layer the green shirt over the white shirt and belt at the waist. Put on brown tights and boots. You're nearly done already.
As for your head, cut your wig or style your hair to appropriate lengths. To make the hat, I tied the green fabric around my head like a bandana and safety pinned in the back. Then cut the remaining sides so that they formed a pointy end and stapled them together. There's probably more advanced ways to make this look more professional, but hey, this is supposed to be an easy costume! :)
For the shield, I used my x-acto knife to carve it out of the foam board. One piece of foam board is plenty, as you can see in the picture, I used the same piece for several other costumes as well. Once I got the desired shape, I referred to a picture of Link's shield on Google Images and painted the design on. I originally had attatched it making handles out of duct tape, but later found a thrift store shield with a better handle and just taped my shield over the top.
Strap it all together, and there you go! An easy costume for under $25 (or less, depending on what's already in your closet.)