There is something to be said for buying a saddle with a "non-offensive," middle-of-the-road flocking job. That being said, the tree *must* follow the lines of the horse's back.
And it's hard! These equine suckers are 3-D. The rat ba$stards change shape with seemingly no regard for our pocket book or love of a particular saddle. They have relatively little flesh-- thin layers of muscle between their skeleton and that of the saddle. We want "close contact." Who thought this was a good design for riding animals? And then we English riders don't go in for the large surface-area of the western saddle which distributes the weight of the rider much better... and increases the margin of error for fitting a horse comfortably. We buy horses for things other than an "orthodox" back... or a back that goes well with our anatomy. Yet we want a saddle to resolve the fit between these two bodies.
But fitting an English saddle to those "non-offensive" specs is a good way to go for man, beast and wallet. It does give you the freedom to do some cheap and flexible messing around with half pads. That being said, I have yet to see a pad that can do the extremely difficult job of exactly fitting the "wither hollows" section or the section from the stirrup-bars to the middle of the seat... where all of our weight is most of the time. It can be hard to evaluate fit in this all-important section of the saddle.
Also, all of this goes better if the rider/buyer gets really educated herself about both saddle fitting and equine management. IME, horses tell you that a problem with saddle fit is brewing long before you have something that another profe$$ional needs to fix. Mine will tell me what's going on in about 3 rides, and they'll be pretty clear about where it hurts and why (it helps that I know some equine anatomy).
If you do some old-fashioned leg work-- commit to paying close attention to your animal and to your ride, you can get along nicely the way people did before the era of custom saddles and saddle fitters.
Best of luck to you all with your saddle searches! Each time you do one, you learn a little more about how to find the next saddle with less muss and fuss.