Welcome back to the horse world...once bitten by "the bug" you never
get rid of it.
Most of the names you mentioned in older saddles are excellent quality.
Stubben, Crosby, Collegiate, Courbette, Blue Ribbon are all excellent saddles and hold their value and usefulness for decades.
Being you don't care about the show-ring fad you have so much available to you to look at.
Try Craigslist in your surrounding area, the Farm & Garden section for horse equipment.
By me, you can buy a really nice used saddle in fantastic condition for way less than you mentioned if you don't care about "fad" today of a split flap look to it.
I would add that unless you can get hands on to check that tree...no sale.
BTW, add Pessoa...the older
Pessoa saddles to that list. Collegiate saddles were made by Pessoa before he started his own company so you bet quality was in his work.
I found most any older saddle with "Made in England" on the pins, stamped in the billet protectors and manufacturers plate were quality made.
That also is something I see in quality saddles is billet protectors provided...cheap saddles don't offer and many have no idea what a must that is to protect the life of your saddle from damages of buckles...
There are so many brands that are quality...and so many names not known because it was from a saddle shops own store brand inventory but made to exacting standards by the really good saddlers.
Judge each saddle on its own or risk missing a great find.
You can keep your "adjustable" and change the "adjustable-gullet" stuff is my personal feeling.
A good saddle will fit a huge variety of horses well. With the exception of a real moose of a horse, those spring trees worked and did their job adapting.
Older saddles are and were made with better leather stock because the cow was older and had time to grow their hide thicker.
In western this is true as it is true in English too...new saddles have cheaper grade of cowhide, thinner and not as hearty.
Older saddles hold up better is a fact.
If you really look closely at saddles you can see the difference in materials used and of course our better craftsman who have retired/died and been replaced over time...there is a great difference.