You've found an amazing contracting opportunity in Mexico, but it's not as simple as signing a piece of paper and making the move. Contractor payroll in Mexico is an administrative mess if you don't know what you're doing. The requirements vary greatly based upon a number of factors. It even varies based upon the country you live in.
If a tax agreement exists between Mexico and your home country, different rules apply. You must also take into account how long the contract is and how long you'll be staying in Mexico. Both affect how much tax you'll pay. You have to understand all this and more before you can even negotiate you final contract terms.
If you plan to contract in Mexico often, you could take the countless hours necessary to study all relevant tax and payroll laws. You could also choose to focus more on finding the perfect contracts and let experts handle all the administrative stress. The last thing you want is to not comply with Mexico's payroll laws. You also don't want to work hard only to earn a small percentage of what you thought you were going to make.
Umbrella companies are the answer and a contractor's saving grace when contracting in Mexico as they do the heavy lifting so you can focus on the job.