Leaving aside what seems to be the most common form of finding a living here for "gringos" being English teachers (which I doubt will be a good idea if you are not already prepared for it and even then not so much from what I hear), or dog walking (seems to be a lot of those) the only things I can think of would be some types of manual labor. Construction (though can be very seasonal), vegetable stands, washing dishes (horrible pay usually), "chinese" supermarket stocking (also usually not very good pay) and things like that. Start for many of those might be around $5000 pesos these days (I remember when it was 3-1 exchange, many of the chino restaurants and stocking positions paid 600-800 pesos!).
I have family who live on as little as that, and as much as 10,000 pesos a month for having worked in some of those jobs for years.
Others may have better ideas, but now isn't the exact best time to be searching for work I think. I remember some people here talking about working at phone centers, but I never heard a single person who did that who didn't feel ripped off in some fashion related to actually getting paid.
Once you're here awhile could be a completely different thing. But nothing I can think of that would be quick, unless you have some specialized skill that is needed here.