There is universal advice that usually come from most people although I do not agree with it 100%. The advice I'm referring to is the one which is "use few % of your salary only". I do not agree because if we use a specific percentage from salary, it can be both something too much (for those with huge salary) and something too small (for those with low salary). For me, the best gambling budget for every individual is obviously subjective and the gambler should know themselves on how much to spend based on many things (not only based on salary).
I think it's perfectly normal when you can allocate your gaming budget relative to your monthly income. You’re right that different people have different budgets, but it doesn’t matter as long as a person can afford to set aside a part of their earnings for gambling. In the same way, they might spend that money on some kind of vacation or other entertainment. A person who earns one million a month will spend much more than someone who makes a few hundred dollars. And that’s exactly why a gaming budget should be formed based on one's income.