It depends.
I used to use the rule of thumb of 50% of the total budget on speakers. That worked well (40%+) until I found a great speaker that could be made arguably the "best speaker on the planet" by actively bi-amping them. Now the actually speaker price is a mere 25% of the total price.
I think that with the high quality of some of the speakers today, the percentage of the total system cost has dropped.
I used to use the rule of thumb of 50% of the total budget on speakers. That worked well (40%+) until I found a great speaker that could be made arguably the "best speaker on the planet" by actively bi-amping them. Now the actually speaker price is a mere 25% of the total price.
I think that with the high quality of some of the speakers today, the percentage of the total system cost has dropped.