Skipping the Last Year of High School in the USA Through Proficiency Tests

[DragonDF]

Ouch, with that budget, you're not going very far...  As I think Franklin is going to be more than a few grand USD, the cheapest online high school charges at least $1500 for the HS diploma... Having said that, there are always workaround options!  My suggestion right now is to get all the ACE/NCCRS credits ready to be transferred into Excelsior or TESU Computer Science degree, you can start with Sophia.org for example, and get all the general education, plus electives, then Study.com etc, until you have at least 90 credits.  You'll use those as dual enrollment credit classes to complete the HS diploma entirely and finish off the degree requirements at either EU or TESU, depending on your choice.

This is exactly what I am planning and said to him. But I need to choose the University option first to be able to study exactly the courses that will be accepted by the specific University. Do you think, because of the age, the best option is TESU or Excelsior for an international student in Computer Science?
 
He needs (like me) to get an English Proficiency Test (Duolingo is the cheapest one) to be accepted by a University in the USA. 

The problem is to spend (lose) time studying for the last year of 'high school' here despite focusing on what really matters. For this reason, I am trying to 'hack' this last year online. 

You'll use those as dual enrollment credit classes to complete the HS diploma entirely and finish off the degree requirements at either EU or TESU, depending on your choice.

About this phrase. 
Do you mean it is possible to do it for how much money? HS diploma (last year)?
Is it possible to finish it only with Sophia? Saylor?
If he studies 12h or 14h / day. How fast can he complete the last year of High School level?

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Not in my state because you need to meet a specific number of credits for various subjects. There aren't exams to test out of the courses. Some high schools have programs with community colleges where you earn college credit for your courses as you're taking English your senior year through the community college at your high school. There are subjects such as PE (physical education aka gym) where you need 4 years of credit in order to be eligible to graduate so skipping a year of high school would mean you're taking the class twice one year if that's even possible as it's not possible at every high school.

If I understood it right, while in Brazil there is a 'second degree' of 3 years, in the USA the 'high school' (second degree) starts in our 9th year and takes 4 years. It is the same number of years but with a bit nomenclature difference in the high school x second degree. 
Especially because in the USA you have a lot of elective courses and in Brazil, the Prussian school is more Traditional: same for everyone. You can not choose any courses.

He is in the LAST YEAR of the high school. Just one year to finish it. It would be very nice if he could do a proficiency test (for this last year) in the USA. 
At the same time he is studying Bachelor's Degree in Systems Analysis and Development at a University here.