The first PC I ever bought was £1000 from a long since defunct Evesham Micro. It was a good machine in it's time & to this day, I still use the Cambridge Soundworks 5.1 speakers in my home media set up, but upon opening the box up, out of curiosity more than anything else, it dawned on me that these things are no more complex to assemble than Lego.
After that, I never bought another pre built machine & I doubt I ever will. It's too easy to build and get the exact spec. you want.