Increased cost likely has little to do with availability and moreso with Apple desiring to keep the high margins they historically have with their products, especially the iPhone. This is pure economics--Apple is setting the price based upon the expected demand from their customers and what they're willing to pay before adversely affecting that demand. If they could sell all the iPhones they produce at $1000+, that's what they'll charge. If people would stop paying these high prices, we'd eventually see the prices come down.
Based on all reports over the past year or so, this simply isn't the case. There's a worldwide shortage of available, quality OLED displays. IIRC, part of the reason Google has partnered once again with LG on one of the upcoming Pixel models is to secure hard to get displays and LG is one of the two biggest producers (after Samsung, of course). And yes, there are lots of phones with OLED displays already but only those on the Samsung flagships are considered the best quality and asany smart business would do, Samsung is reserving those panels for themselves first. Also, you can't start stockpiling displays years in advance--the technology is moving far too fast for that and that's also just poor cost management--you don't want to have large amounts of unused inventory sitting in warehouses somewhere, especially inventory that will likely be subpar quality or obsolete by the time you actually need to use it. Even though Apple could certainly afford it, that's still the equivalent of just setting your money on fire.
