If you are fairly certain of your shoe and hat size, our Applejack had a good deal of luck on Amazon.com. That style of hat was quite popular a few years ago, and is still available for pretty cheap. I suggest searching for "straw cowboy hat".
Alternately, for both hat and shoes, check places like Khols and Target, if you want something Brick and Mortar based (as opposed to online). Kohls has amazing clearance sections of things - and they had cowgirl boots for under $10 a few weeks ago, at the one near me.
Let me know if you want particular links - I can dig up what I can and let you know.
Ok - I did a little digging, and found a few inexpensive hats:
Hat no. 1
Hat no. 2
I ahve horrible taste in shoes, so you're on your own for finding cute ones. But Amazon has a lot under $25
Convention Line-Up: BronyCon 2015 - Dragon*Con 2015
1950s Celestia (MLP:FiM), Undead Death Knight Starter Gear (WoW),
Lorna Dane Serval Industries (X-Factor), Adult Loki (Loki: Agent of Asguard)