My kids go to the CE Ingenieria in San Miguel - there are various campuses around Lima. It is a math intensive school - our older son is in 2nd year of secondary, each week he has classes in Arithmetic, algebra, geometry, trigonometry and reasoning. They also study physics, chemistry, biology, literature, psychology (!), economy and philosophy, as well as your regular classes like communication, civics and history.
The cost is going up to S/220 per month next year, which is very reasonable. The school uses it's own books, which cost S/200 at the beginning of the year.
The only complaint I have is this: because the price is so low, they don't pay their teachers well, and they have a high turnover rate. It may bother others that the school (in San Miguel, anyway) is in a small, old building without a lot of upkeep. But, they have a reputation for sending lots of kids on to uni, so I guess they're doing something right.
If I could afford it, I'd send my kids to Trilce
which is very similar in program and has a good reputation. They also have campuses around Lima, including one on Benavides here in Miraflores, walking distance from my house.