If you’ve been directed here, it’s for voluntary payments for favours which are done outside regular classes. Regular classes should all be paid for in the normal way.
Here, you choose how much to pay. You’re welcome to buy me a coffee, cook me dinner or collect me from the airport at some future date as an exchange rather than make a payment in pesos.
Don’t know how much to pay?
It’s your choice.
But if it helps, you can imagine that I can translate at 300 words per hour or write at 500 words per hour (if no research is needed, and I’m comfortable with the topic). To quickly read and comment on a text of 500 words might take 20 minutes. Editing takes longer, especially a detailed edit with suggestions and comments. Proofreading – which doesn’t change the text but only corrects things like punctuation and mistakes – could take another 10 minutes for 500 words.