Last year for Halloween my then two year old wanted to dress up as a 'train'. I convinced him to be an engineer and steer the train. I was too cheap to buy the engineer hat that I saw in the store so I ran a search to find a free pattern to make one. I hit the jackpot. I found a tutorial here at Mushroom Villagers with detailed directions and pictures too! It was pretty simple to make and only ended up costing a couple of dollars. I used heavy weight pillow ticking from JoAnns and of course bought the fabric with a 40% off coupon. I'm very happy with how it turned out.
The train costume was first made for my oldest son when he was 4. Yes, I saved it (under the stairs) in hopes we'd be able to use it again. I couldn't stand the thought of throwing it away. I'll post sometime about how I made it. You'd be amazed at how simple it is.
Edited to add: Click Here for a tutorial on how to make the train costume.
I had so much fun making the Eddy cap for the costume I wanted to try one for my daughter. It was even easier this time because I learned a little trick when cutting it out, that saved me a lot of time. Follow the tutorial, but when you cut out the bands, cut them the same width. This will allow you to turn the edge of the band under and stitch it with the machine so you don't have to handstitch anything.
I was very excited with how easy and cheap it was. This hat cost me $1.50 to make! I had the flower and interfacing already and I used 40% off coupons for the fabric at JoAnns.