For digital playback, I spend ~30% on source and DAC, another ~30% on speakers, and the remaining on preampfification, amplification, and cables. That ratio has served me well in multiple system setups. There's never been an obvious weak link.
However, everyone has made good points about finding "your sound". I recently violated my rules and acquired speakers that are only around ~10-15% of the stack cost. They were special to my ears and brain so, even if you adopt a ratio, you may end up violating it anyway down the road.
The common denominator here is, buy what works for you.