I live in Australia, used to own a Bates Kimberley Swinging Fender, have ridden in a TON of stock saddles, and am currently getting one custom made for me and my horse, so I know a little bit :]
Firstly - MOST of the cheap saddles on ebay are just that. Cheap, cr*ppy quality, bady fitting, so on and so forth :]
Firstly, decide if you want a swinging fender or a traditional. A swinging fender is sometimes called a hybrid, as the swinging fenders are the same/similar to the stirrup system on a western saddle. The traditional saddles have an english type stirrup set up. They are different in terms of the range if movement and support for your leg. I found the swinging fender gave a lot of support, and a fair range of movement. The traditional gives you more movement but not as much support. Another thing to consider is where the stirrup bar is hung. It can either be the 'traditional' style, which puts your leg more forward in the style of the old drovers, or the newer 'centered seat' style, which brings your leg more underneath you, in more of an english/dressage leg/seat position.
I have NEVER seen a stock saddle in Australia with a horn. A horn is only added to cater to western riders who want it. A TRUE stock saddle doesn't have a horn, it would inhibit a rider in sports such as campdrafting.
Now, the big one! Price. With stock saddles, you really do get what you pay for. Try to steer away from saddles called 'Kimberley Poley', they tend to be cheap indian imports. If you are looking on ebay, you can often find cheap second hand Syd Hill saddles, which have a good reputation in AUS.
One more thing... A lot of stock saddles out there sit you an inch or more OFF your horse. I personally hate these saddles! I prefer a close contact saddle. I like to be able to feel what my horse is doing and communicate clearly with my seat.
A lot of people on this forum have had success buying through a website, I forget the name, but they sell a saddle called the 'Longreach'. Try googling it. They aren't the quality of a lot of the good saddles here in AUS, but people on here who have bought them have been happy with them.
There is also a saddlery called 'James saddlery' who make saddles in AUS and can ship to the US, they sometimes have specials and packages available.
This is a saddle made by coopers saddlery
. He makes really good saddles, pricey, but worth it. This is a good example of a GOOD quality, balanced, close contact stock saddle. He has a really good FAQ about stock saddles and swinging fender vs. Traditional, click the link above if you want to have a look.
Feel free to PM me of you want anymore information :]