Meshilicious case: $150 (little extra for the mods)
4 Noctua fans: $125
That means everything without the GPU is $1235. I have no idea what a 4080 costs these days, so if you think $515 is a good price for it, then I'd say it's a good deal.
ETA: Even though AM4 is EoL, a 5800X3D will serve anyone well for probably 6-10 years.
I honestly would contest the price for the ryzen because sure thats how much you pay for a new one but at the same time there are ryzens (am5 sadly) out there that have a lower power consumption, same or better performance at the same price. Another contention would be the hard drives. I would personally never use second hand storage, mostly because i am a paranoid fuck wit, but for me a used drive is at most worth half a new one as soon as someone puts their filthy data on it. But yeah the 4080 is still pretty expensive.