Are ITX builds really considered expensive? I mean, the higher end motherboards are certainly expensive but the same can be said about premium motherboards in general. The cases are about the same price as standard cases, and the same can be said about coolers. Really, the only thing that really is more expensive would be the PSU, but there are plenty of ITX cases that accept an ATX PSU.
You aren't wrong on that front. It really depends on what is important to you and your budget. The cases can range from $30 and go above $200 if you want the niche cases like the NCASE or the Dan-A4 SFX.
For me personally, I ended up getting a Corsair SFX PSU since the case I picked out(NCASE m1) was pretty small and using an atx power supply meant only having about 7 inches for the video card and no place to route cables. In addition, I picked out the z270i Asus itx board to have two m.2 slots for my NVMe drives. Decided to get a AIO water cooler for the cpu so that added on.