Dover is always my go to place. Shiloh tack is a great place to find awesome deals as well. I just bought a beautiful dressage bridle from them for $30. I figured if it didn't work out, it's just $30. No big deal. But it has been great! Very supple and soft.
I am not an expert but you can get great deals on used equipment on a Facebook group called English Tack Trader :)
I would recommend a Cordona saddle, which is comfortable enough :)