Assume you earn $24,000 in a year.

i.e., $2000 in a month.

If you spend, $500 on transportation:

500/2000 = 25% of your earning and you are only left with $1500 to spend and save.

On the other hand, assume you earn $240,000 in a year

i.e., $20,000 in a month.

If you spend, $500 on transportation, i.e., the same amount as previous scenario, it is only 2.5% of your earning. You are left with $19,500 to spend and save.

$500 spending on transportation (real terms) is different for the two scenarios. It is always a good practice to look at the percentages