OKI am researching how to build a system from scratch.
Here is where to spend your money:
Speakers.
Amplification with sufficient power (depends on your speaker efficiency, and your listening distance.
Pretty much everything else can be audibly perfect at low cost. Think wiim range for streamers, and if you need a separate DAC you don't really need to pay more than around £$250. Though with the Wiim pro plus, or the Wiim ultra you don't really need one.
One other thing to consider would be DSP for room correction - this can make a big improvement to the sound quality. Wiim devices can (to a certain extent) do this also.
Where not to spend your money:
Power generators and similar
Cables - beyond the basics of being robust enough, and (for speaker cables) with sufficient cross sectional area. If you are spending more than around £$20 on a cable, you are probably spending too much.
Expensive digital electronics (streamers, DACs etc). Pay for the features you need, but not for sound quality - which is a solved problem even at the low priced end of the market.