To JB’s point…
An Appendix is technically a first generation TB/QH cross. AQHA will give that horse a registration number starting with a X. But there are LOADS of them out there that are technically not Appendix, but have a fair amount of TB blood. My gelding is about 16.3/17h, big bodied, athletic, good minded; he’s awesome. My barnmates like to play “guess what breed he is” if they have friends that stop by, because he doesn’t look what what most people expect for a QH, nor does he look like a TB. But he’s a HUS bred QH; by a western pleasure stud and out of a Sky’s Blue Boy mare. She’s technically not Appendix - but SBB is, as is her mother, so she’s still half TB, but not an Appendix. All clear as mud. So my 100% QH gelding has 1/4 TB blood. So if you’re on something like Dreamhorse, you may have to search just QH.
I’m not surprised there aren’t many HUS bred horses in OK, but head to TX and you’ll find some, as well as on the east coast (tons in OH…). HUS/English bred horses just aren’t terribly popular in the west & midwest. But I have seen some pop up in areas like CA & AZ that are super nice, and well priced, but they’re still going to be alot more than an OTTB. With that said, you can probably find some prospects not terribly expensive that could be competitive at lower levels. Technically the AQHA HUS class was suppose to be a training class for over fences. However, it’s definitely it’s own specialized discipline. There are alot of horses out there that can’t be competitive at AQHA shows in HUS, but can certainly go on to be successful in other rings. Since AQHA o/f isn’t super popular, some of those horses hit a dead-end if they can’t make it in the HUS ring. I sold a 14 yr old HUS flunky to a family a few years ago. Family with 3 girls looking for a low level hunter for local/IEA shows. I run into the trainer that helped with the deal periodically - she loves the HUS flunkys in her program and always tell if any of my QH friends want to sell, to call her. On the east coast, I’d say expect to pay somewhere in the ball park of $7500 - 10,000 for one of these QH depending on age, location, etc. Young & very green will get you there for less, but still more than an OTTB.
Tori Colvin has been posting videos of Out of Vogue, an Appendix buckskin gelding, on FB from Wellington. Tori raves about him on FB, when I’m sure she has a stable full of uber fancy WBs. His owner is also the breeder - using her QH mare and a TB stud. Whew-hew for the home bred Appendix! 
Another thought, if you willing to shop auctions, checkout Professional Auction Services. QH people that run very reputable auctions (previously was live, now online), but with some looking, you can probably score a nice appendix for a good price through one of their auctions.
