There are too many variables for there to be any reliable ratio of how much to spend on any component based on the price of another. Points of diminishing returns will vary for each type of component so If you're spending 3k on a system you might spend $200 on a dac and $200 on an amp because the difference between speakers that cost 1k and 2.5k is huge and the difference between <1k amps and dacs is small. On the other hand if you're spending 50k maybe you spend 25k on speakers, 15k on an amp, and 10k on a front end because more expensive speakers tend to need a lot of power and quality power is expensive. You want a front end that looks nice and will last 30 years.
The ratio at given price points may be somewhat correct at a particular point in time but it could change radically. Low cost, perfect amplification might be a solved problem or may be soon. What if class D measures perfect and then some company goes and buys the most expensive amp and makes a cheap amp that adds the perfect distortion so that nobody can discern it from the most expensive one?
What if you like high sensitivity speakers so you hardly need any power? That messes up any formula that would apply to low sensitivity ones. Maybe you prefer vinyl, that would wreak havoc on any formula meant for digital. What if you listen to string quartets vs. hard rock. Totally different priorities. This is a situation where there are too many variables for it to ever some down to a simple formula or price. That's why it's a hobby. It's also about people watching because a big part of the population can't handle the ambiguity and engage in all sorts of amusing behavior to ease that pain.
