If you want to play it completely safe, I would contact the organization putting the show together. :)
If it is a schooling show, typically a schooling pad is okay, and a polo shirt, breeches, and tall boots or half chaps is "dressed up" enough. Others are even more lax, but to be safe, I would go that route. For western, long pants and a button up or even the polo from your English classes.
If it is simply a smaller show, but not a schooling show, I would use a nicer pad, either a square jumping pad or a fitted, fleecy or sheepskin pad if you are showing hunters. You should wear a coat and a shirt with a ratcatcher or tie, breeches, and tall boots. Your western attire is less bound by tradition: you could wear a button up, your hat (or helmet), and long pants, or add chaps/chinks, or even wear a fancy rail shirt or jacket if you have one. If you are on a budget and don't have the attire, though, I would go for a button up in a color that compliments you and the color of your horse. A newer trend is to add a little neck scarf to this look - it's very sharp! - which is an inexpensive addition. You may be able to find a saddle blanket or pad that matches this shirt - Mayatex makes some 'cheaper' options in many colors, that should hold up if you aren't showing every weekend.
Your halter look typically depends on the type of horse you are showing. If it is a schooling show, I'd say your same outfit will work fine. A smaller show, business casual (blazer, long pants) is a safe bet, unless you know what attire is appropriate for your horse.
To save money, definitely look at consignment horse show shops! (I once found a beautiful hunt coat at the Goodwill!) Or, even Walmart, Target, etc, sell things like long pants, blazers, button ups...
Last edited by Little Mare; 08-22-2013 at 12:04 PM.