At a show this summer, the sole of one of my boots was coming apart. By the end, my shoe had a mouth! I felt like everyone knew it too. I am taking a break from showing this fall, but wanted to be prepared for late winter/spring shows, so when a pair of field boots at a local tack shop went on clearence, I snapped them up. The calf was to slim for me, so I had the leather stretched by the store. The alterations only cost me 45 dollars. Finding reasonable show clothes can be done! Take a drive to the area tack shops and look around. You'd be surprised what you find.
Anyway, I went out and ordered one (had to get a different color since all I have was a black coat for dressage - my main discipline of choice so far has been Eventing), because I wanted to look the part for any hunter show I might do. I didn't want to show up in a black coat when I know that hunters are traditionally gray or navy. I'm not saying go out and buy a whole new wardrobe, but like HeartMyOTTB said the sales are out there, you just have to look for them. Looking the part is a part of the show itself. I know that in Eventing some may think it's not quite as "strict" as hunters, but really at the higher levels it has the same amount of "strictness" in the dress code.
I think lower level anything you can get away with more, but most don't want to, they want to look their best if nothing more but because it makes them feel more confident which will radiate out to the judge.