Well it's really a matter of how much are you willing to spend
Say for pedals I think the lowest you would want to go is CSL Elites, they're the cheapest load cell pedal set around as far as i know, next step up would be the CSP v3 or from there what I run are HE Pro pedals (currently on sale atm I believe). The advantage of going higher end is the resale will always be good if you pack it in after a while and the quality and durability of a set like the HE Pros is awesome.
For wheels there are a lot of options, I still use my old CSW v1, the CSW v2.5 is probably the best non-direct drive wheel you can get. Thrustmaster wheels are pretty common around here, the TS-PC is close to the CSW from what I understand. If you want to go high end for a wheel then direct drive is where it's at nowadays. I've pre-ordered a Fanatec DD1, it's probably the most cost effective DD wheel for us here in Australia, otherwise you're looking at building your own OSW wheel or buying an OSW kit from overseas (or there are a few local options too).
For a PC it kinda depends but for iRacing single threaded performance is most important, particularly if you use VR. If you run a single screen or triples then a regular Intel i5 or Ryzen chip will probably do. If you use VR then you need something like an 8600k overclocked to around 5.0GHz, I personally have a 7600k at 5.0GHz. The i5 is all you need, the i7's will not help in iRacing, the 8600k is probably a more future proof option as it has 6 real cores vs 4 that I have, it makes no difference right now for iRacing but could in the future.
I use a GTX1080 for a GPU, I don't believe there's really any need for anything more in iRacing in any scenario, a 1070 would probably suffice.
Other games will be a bit different but I don't run anything else so can't really comment. Something like an 8600k will be good for anything but other games might benefit from a better GPU.
For someone starting from scratch and wanting a really kick ass setup I'd say you're looking at $6k+
~$1k - Pedals
~$2k - Wheel (base and steering wheel)
~$2k - PC
~$700 - $1.5k - Monitor/s &/or VR
~$1k - Rig and extras
It's actually a bit scary when you lay it out like that, you can drop that quite a bit
~$1.2 - $2.2k - Fanatec bundles including pedals, base and wheel, CSL level through to CSW level
~$2 - 2.5k - PC/Monitor/VR
~$500 - $1k - DIY Rig and extras
So maybe around $4k for mid/good quality range and not that you couldn't save more either.