Is there a magic formula for spending on components in a system

I forgot to add in laptop and mic for measurements. Most already have a laptop and you can get a good mic for $75. You might need more for Room than I spent. My room was already pretty dampened and restricted on what all I can do since it isn't dedicated. IMO speakers and room are your most important considerations. Invest the most in speakers you like it's easier to upgrade the other items unless you have enough money to get everything you want at once. 

For my system.
1. Speakers $10,000
2. amplification including DAC $4000
3 .Source digital <$1000
4. cables<$200
5. Room $300

Is there a magic formula for spending on components in a system?  Even better: there are many such formulas, each with its adherents. And each formula is right for someone.

In other words, I agree with @almarg on this.

I agree with those above who stated there are too many variables. 
The greatest ones are your total budget and the efficiency of your speakers.  I have two sets of Magnepan and ended up spending a lot more on power amps than I would have spent on efficient speakers.  
However,  for the past 25 years, I appear to be addicted to Maggies.  

Try this to assess the sound in lieu of measurement gear:

https://ohmspeaker.com/news/thinking-outside-the-box-listening-outside-the-room-or-the-bouncing-sound/

Percentages have gone up and down I’ve the years as I’ve upgraded this piece or that. And, I use new prices to calculate tough many pieces have been purchased used. That said: 20/30/30/20 percent, for source/amplification/speakers/cables. There’s no turntable in my system—it would certainly be more for the source if I was into vinyl.  And cables are usually bought used or on sale...again, I’m comparing list prices for new equipment to come up my magic formula (hey, at least it’s easy to remember).