I’d go with the dressage saddle.
In the english saddle world, there exist entry-level saddles that can fit a horse and put a rider in a good position.
In the western saddle world, the real quality saddles (used) that will put you in anything more than just a sort-of, average position are expensive. In my opinion, entry-level western saddles do not exist that will do your riding/seat/position any favors. If you do go that route, there will probably be some consequences in terms of un-learning some body memories.
You might find a good used (plain, rough-out, no tooling or silver…in other words, a bit homely) Wade saddle-a real one, that puts you in a dressage seat- for $1500. McCall is a good brand there. Otherwise, you’re looking for a handmade saddle, on a handmade tree, and $1500 is going to get you something fairly old and probably not great to look at-though if it doesn’t need repairs, I’d sure go that route. And you can find handmade, non-Wade saddles that have a great seat in them, they just aren’t as common.
My mom has my Billy Cook saddle, an OK made one, and it is definitely a quality saddle. It put ME in a bit of a chair seat, but Mom has a bit bigger sit-upon, so her pelvis is further forward over the stirrups, and it puts her in a nice dressage-type seat. But…she really notices the difference when she rides in someone else’s quality Wade saddle. So anyway, $600 to $800 can buy you a well-made saddle that won’t get you into position trouble, if you look around, and give you something with a useable horn. My Billy Cook is heavy, and has a bullhide-wrapped wood tree, and you could rope off it. But a lot of $600 western saddles are made on some sort of flex tree or lightweight deal, you don’t want to actually use the horn for more than a hand-rest or grab strap. Even if you never rope live cattle, getting a horse good with a rope, with dragging railroad ties and such, is really, really good for the horse, and for making a broke one.
I wouldn’t go Aussie, those saddles are designed particularly for the rider to put his feet forward and brace against the stirrups:
http://www.downunderweb.com/store/media/RIDING_POSITION.JPG
So really, for the $$, I’d find a nice used dressage saddle, unless you need a saddle horn or must have a western saddle for any particular showing/competing.