Typically the $1000+ premium phone market is for unlocked phones sold directly from the manufacturer.
The locked phones are usually sub $250 and have some kind of finacial gimmick to get the sticker price lower. Often it will be some carrier specific model name. Just sort by price low to high and you'll find them.
ATT, Verizon, and Tmobile are selling many many expensive phones, locked, on 24 momth payment plans, literally hundreds of possible configurations of dozens of models.
Or is there some carrier that sells the expensive $1000+ phones on prepaid plans?