It depends on one's income. The more you can afford, the more you can spend on gambling. But we should not spend more than 3-5% of our income on gambling.
Even if someone have a big income, he can not use too big money to placing his bet. He must adjust his income and know how much money he will use to playing gambling. The important thing is you only need to use the money you can afford to lose to playing gambling. You will not playing gambling using too much money because you know the risk behind that. You can prepare some money you will use to playing gambling and will stick to that while you will not add more money to playing gambling.
I think yes for the issue of income it cannot be used as a benchmark, meaning when for example your income is quite large it does not mean you have to bet with a large amount too, in the end of course as you think that for this problem it comes back to the readiness of a gambler regarding how much they are ready to lose regardless of how big or small their weekly or monthly income is. On the other hand I usually measure it by percentage, meaning no matter how much my monthly income is I usually only allocate no more than 5% once a month.