In thinking about it, these questions are probably better answered on https://expatriates.stackexchange.com but I'll answer here anyway. Maybe someone will move the question across to that site.
Salary/Travel Expenses
The amount of travel expenses are on the low side for US government recommendations for Georgia as per FY 2018 Per Diem Rates for Georgia. However these rates are based on staying in a hotel and buying every meal at a restaurant. But if you are staying for an extended period in your work location, you should be able to obtain a lease on an apartment etc that will be cheaper than a hotel room - which also allows you to cook your own food for cheaper prices etc. You need to look at hotel and apartment prices in the location that you will staying to see if these travel expenses make sense.
The salary of $USD1000 is very low for the US, but it may be more than what you would get in Mexico. And this is the equation the recruiter is looking for - pay you more than Mexico (but way less than the US), but charge the client less than US rates and profit from the difference. It is up to you to decide if this is acceptable - however I would try and push for more money. But remember that the more they pay you the less profit the recruiter makes.
But as per the comment from bharal, you will also be gaining valuable experience. In addition you should be making valuable contacts that could help you move-up to a better paying position (EG you might be able to get future employment without using this recruiter and hence make more money)
Visa
I am concerned that the recruiter has been vague about the class of visa you would require, because if you are a Mexican national you are potentially eligible for Visas for Canadian and Mexican NAFTA Professional Workers
The nonimmigrant NAFTA Professional (TN) visa allows citizens of
Canada and Mexico, as NAFTA professionals, to work in the United
States in prearranged business activities for U.S. or foreign
employers.
However you still need to fall under one one of the defined categories. From the job description I think you might fall under:
--Computer Systems Analyst--Baccalaureate or Licenciatura Degree; or Post-Secondary Diploma (3) or Post Secondary Certificate (4) and three
years' experience.
(3) "Post Secondary Diploma" means a credential
issued, on completion of two or more years of post secondary
education, by an accredited academic institution in Canada or the
United States.
(4) "Post Secondary Certificate" means a certificate
issued, on completion of two or more years of post secondary education
at an academic institution, by the federal government of Mexico or a
state government in Mexico, an academic institution recognized by the
federal government or a state government, or an academic institution
created by federal or state law.
Note that I am not qualified to give legal advice on Visas. But if the recruiter suggests that you work under an inappropriate visa then I would walk away from the offer as the penalties for visa fraud can be very strong. EG Up to 10 years permanent ban from the USA. I would suggest consulting a Visa specialist not connected to the recruiter in order to evaluate the eligibility of your application.
Note that part of the eligibility of this visa category is that you have:
.. a contract or employment letter from your employer in the United
States confirming your upcoming employment..
This says to me that you can only work for the one company and that if you quit or your contract is terminated, that you have to return to Mexico (Note again I am not a Visa specialist).
Non-compete
You have said that you will be employed by a Mexican company, so to me that means any non-compete clause of a contract would be adjudicated under Mexican law. So there would be no restrictions on working for other US companies - as long as you can get employment with them! However, again I recommend you get legal advice from a professional in Mexico.
Taxation
You didn't ask this in your question, but taxation is an important issue and can have huge financial consequences if you get it wrong. You may be eligible to pay US or GA taxes depending on where you are paid. (Again I'm not a tax specialist .. blah blah blah). However if you are solely paid in Mexico, to a Mexican bank account you may be able to side-step paying tax in the US.
And if you can structure it correctly you might even avoid paying some taxes in Mexico assuming there are legal loopholes. EG In the US money paid as travel expenses is tax deductible up to the amount specified in the Per Diem tables. So if I was paid $USD93 per day for accommodation and $USD51 for Meals and Incidentals, but I only spent a total of $72 per day on those items, I can still claim the full $144 per day as a deduction - thus effectively giving me $72 per day tax free.
