7 small books for IIT that will cost you less than Rs. 500 or 1000 in total

Hello there. We will start off with the suggestion for list of books you would require for preparation for JEE ADVANCED or for just having fun with mathematics. We will provide you with a list that you will get for a very very low cost at any old book store and i guarantee you that these will be sufficient in preparation for jee advanced.
First with basics:-
1. NCERT for class 11th       2. NCERT for class 12th
Topic Wise :
Trigonometry:
1. Trigonometry Part-1- S. L. Loney. We do not need to do whole book. But, we do require to do a good part of it. Whole of trigo syllabus is covered in this.
Algebra:
1. Higher Algebra: Hall and Knight
2. Higher Algebra: Bernard and Child
The combination would be really good.
Co-ordinate Geometry:
1. Co-Ordinate Geometry -S. L. Loney
Whole syllabus is covered in this.
Probability:
NCERT of class 11th and 12th covers all of the required basics for solving the problems of probability. And do not worry, the problems of probability are easy comparatively and more lively.
Calculus:
This is topic that requires great practice. Other than NCERT, you will require
1. A problem book in mathematical analysis. - G. N. Berman.

If you have the above resources, they will prove to be more than enough for jee advanced preparation.
To perfect yourself, you can practice monthly magazines of mathematics today and mathematics spectrum. This is the maximum that anyone can/should do. You are not going to need anything more than this to get the maximum marks possible in maths section of jee advanced. That would be my recommendation.