Haha... Most hardware shops now even have special section for cryptocurrency miners ..
I've bought also some top of the line 700$ model of GPU from nVidia because I had to run some statistics computation in parallel.. After about a year I was done and didn't need the GPU card anymore I sold it.. The funny thing is that I sold it for more than I have bought it, because out of sudden, prices increased due to some scarcity of chips .. So you never know, maybe it is good investment.. haha..
Sure, I always build my own PCs from custom components. I prefer to know what exactly components and brands I'm using.. You can also learn a lot in the process and once you've got some experience there is no problem with hardware that can surprise you (and you can save on repairs).
Lately I prefer to build specially quiet and well cooled PCs to serve as home server and media station. For this I can recommend great PC cases from Thermaltake (e.g. Versa) and cooling from Noctua (e.g. NOCTUA NH-D15). These can be tuned so it is all low speed and quiet and at the same time provides sufficient cooling to extend life time of all temp sensitive components (CPU, HDDs, SSDs).
And I've also learned not to underestimated regular maintenance like cleaning inside, washing dust filters and keeping all vents in proper shape. That really helps to prevent overheating and have stable system (of course using Linux) with longest uptimes.