One of your links fails to work for me, but I think you are asking a question which is difficult in that what one person finds acceptable another would reject.
Most high end gaming machines that "wouldn’t be outdated in a few years" will cost quite a bit more than the top figure you quote. Cheaper units may well be noisier as well.
Perhaps your best bet would be to look at a few more suppliers such as click here, consider what your real requirements are and then search the various sites to identify prices. If you have a decent computer store where you could try various models this may also help.
I also think the general opinion is that self build is not any cheaper than buying. Perhaps the major advantage would be that you could customise the build to exactly what you want.
Hope this helps.