For the present plural, "¿Cuánto gastan?" means "how much do you all spend?" For the past tense (did), the singular would be "¿Cuánto gastaste?" or "¿Cuánto gastó usted?". The past plural "how much did you all spend" is "¿Cuánto gastaron ustedes?"
As you can see by this example, Spanish conveys a lot more information in the verb conjugations compared to English. Seeing the conjugation usually makes it clear who is performing the action, and in what tense, without having to supply context.
gasta mucho
.2 dollas
Less then four months.
gastar
Translation: 'Pasar' or 'gastar' (tiempo) = to spend (time) gastar (dinero) = to spend money
How much money DO you spend?
How much do you want to spend is "¿Cuanto quiere/quieres gastar?" Quiere is used if you are speaking formally (to someone older or of higher position than you) and Quieres is used if you are speaking informally (to friends, siblings, etc.)
As much as i can afford to spend
Gastar is Spanish and Portuguese for spend.
yes they only have as much money as they get to spend, they can't spend extra money.
How much spend money
Too much. I spend around $600 per year.