I know this post is a bit old so maybe you´ve already moved, but I just wanted to put in my opinion.
I´ve been living here for a year and a half teaching English, and I mean ONLY teaching English, I don´t have much savings. I can tell you it is possible to live on as little as 1200 pesos a month, which I have done, but it is not recommended...
Therefore I reckon that on 3500 pesos you should be quite comfortable. I currently live on around 1400, but I have a flat with my boyfriend (who is from here) so I pay 500 pesos a month for rent. I´ve rented rooms in many shared apartments or houses, and you can find rooms as cheap as 700 pesos a month...which are not recommended, since there is usually SOMETHING wrong with them if they are that cheap. Go for one around 1000 pesos a month, since you can affordit. You will be so much more comfortable. Also, for just a little more, maybe 1500 a month, you could probably find a temporary rental furnished studio apartment, if you prefer to live alone. But the house share is a fantastic idea to practice the language and to meet people and get advice about the city, etc.
As for teaching English, it is not hard to find work, but it depends on many factors. Do you have any certifications or qualifications? If so, you will find more offers than you can handle. If not you´ll find work anyway, but perhaps somewhat less easily. Be prepared to make no more than 25 pesos an hour if you work for an institute, and if you want to teach private classes, you can probably charge betwen 30 and 40 depending on your experience. It´s not a lot of money - but if you´re living on the rent of your flat, you´ll be very comfortable and you´ll enjoy your time here. Teaching English is a lot of fun if you don´t have the stress of money to ruin it!!
My email is
[email protected] if you have any questions feel free!! I hope you end up coming - it will be an unfortgettable experience, for sure!