I'd say get a jacket pattern and just build it from scratch. Joanns is having a fabric sale going on with two coupons for 50% off regular price. The cheapest cotton you can buy (with many colors) at joanns is symphony broadcloth. It's 100%, thin and just sucks overall in quality, but it's cheap at only 3$ a yard. With 50% off, that's $1.50.
Depending on your size, you'd only need 1 yard of blue for the main body and then half a yard of white for the sleeves and collar. You can also invest on interfacing for the collar, but that would make you pay for interfacing. I say just let it be flimsy and don't even bother to face it if you want to be really cheap.
Also, you'd just need some yellow double fold bias tape which is 1.50$ for 3 yrds.
If you don't want to buy a pattern, just trace the seams on a jacket or button up shirt you already own and there you have it, a free pattern.
Since you're building everything from scratch, it'll be quick and simple and you don't need to worry about modifying.
As for the hat, just use fabric paint to paint on the green design. Heck, if you want to be really cheap, use acrylic paint, only like 29 cents at Joanns