You need to know what goodhorse asked- what type of harness does the rules of the organization you will be showing under require, and what is in fashion as well?
Don’t spend less on a harness than you would on a saddle. The price ranges are pretty similiar.
Light harness as would be used in Appalooa breed classes, or in pleasure driving classes at open shows that follow AQHA rules, sells new for $2000-$5000 these days. Harness prices have gone up, you used to be able to get an entry level Walsh harness for $800. Light harness does not have breeching, does have an over or side check (the use of which is optional under Appaloosa rules), does have a breastcollar, is black leather trimmed with black patent and colored (usually red) leather and brass hardware. Now before you go yikes! look for quality used! Top of the line is Freedman, Hunt’s is a close second, then Walsh. Smuckers makes (or made) a light show harness but it it is a distant fourth. There are a few other smaller makers that you will rarely see, Kennedy is the only one that comes to mind at the moment. Look for used! Confirm the maker if you can and that all of the parts are there and nothing is broken when you think you found something! People will sell their old harness when it has gone out of style. Right now in the Saddlebred show ring French tugs and tufted back pads are in style. So harnesses with wrap straps and seperate back pad pads are totally out of style and not desirable, but nothing wrong with these styles other than they are out of fashion for showing Saddlebreds, from what I have seen these features are not out of style in the stock horse ring, so what I am getting at is here is wear you can pick up a bargain such as http://denver.craigslist.org/for/3668544316.html This harness looks like an older Walsh or maybe a Smuckers, I would guess it is from the '80s.
Other things to note:
The traces should buckle into the breast collar. Cheap harnesses don’t have buckles between the traces and breast collar because it is cheaper to make that way.
Thin flat straps vs. machine rounded straps vs. hand rolled straps. On light harnesses the thin straps will be made using one of these techniques. Cheap harness will simply have thin flat straps, which are very prone to breaking and are frankly unrefined and ugly. Machine rounded straps are alright. The most expensive harness will have hand rolled straps on all the refined places. When you see machine rounded and hand rolled side by side you can see the difference.
Blinkers and blinker stays. Cheap harness will often have flat blinkers with floppy blinker stays. Flat blinkers leave no room for the eyes, floppy blinker stays don’t stay put, very irritating for the horse. Better harness has a bit of shape to the blinkers and a stiftener in the blinker stays. On the best harness the blinkers are carefully molded.
