Please remember the conscientious ettiquette policy when posting on this forum.
When I bought my first horse, I was 16 and made payments on him. ($500 total). I got him home with a halter and then I bought a $2 lead rope for him.
I went to an auction and bought an all purpose saddle that I used for years in schooling shows.
I rode in dressage events, cross country, and hunt shows all with that single saddle. If you are showing at a local level then an all purpose saddle will do you fine.
I'm not sure where you are located, I'm geussing VA. I have never been to Dover but I know they have a trial that you can do with saddles, you can also look in the horsetalkmagazine and the vaequestrian for used tack.
I don't know of any "cheap" places to buy tack but I know Nokesville used to have an auction (that's where I bought my first saddle) and I think Orange county still has one....
Just be sure the saddle fits your horse. If you can't have the horse with you, you can take a metal hanger and bend it around his withers and down to his shoulders to get the outline of his shape. I'm not a TB person so I don't know how hard or easy they are to fit for tack.
Hope that helps...