There is no "Apple tax." Macs are priced in the same range as comparably-equipped PCs. It's just that Apple, by and large, doesn't play in the low-end markets. Closest thing is the Mac mini at $499 US.
The 27-inch iMac is in a class by itself. Price out a high-caliber 5K (not 4K) display of the same size, add a computer of similar capability to even the cheapest iMac 5K, and the PC doesn't come close.