i want to build a Quadrotor helicopter which should cost-effective. and i don't want any complicated mechanisms. i just want a simple one. so could anyone help me?

Please use the search function.  There are multiple threads on this already.

http://www.rcindia.org/search2?search=quadrotor

http://www.rcindia.org/self-designed-diy-and-college-projects/quadrotor-build-thread/

It's been a long time. I was really busy with my exams and i finally got free. I have not started to build my quad-heli. Now am starting.
Recently, My SMPS broke and i had to replace it. I found to see a fan inside it and was wondering if it did any good for my heli's props.
It's a DC Brushless fan DC 12V, 0.15A.
The pics are below.
Suggest me if it's ok.

hallo, sir my english is very poor so i write in roman hindi and english
main ek quadrottor banana chahta hu jiski payload capacity aprox. 1.5kg ho aur uske sath cemra bhi lagana chahta hu  es project ke liye muje kaun kaun se parts ki jarurt padegi
main electronics ka kam karta hu, aur sabi tarah ke circuit dekh kar  assembel kar leta hu pcb banana janta hu abi tak main fm tx- rx ,am tx-rx , cw transmitter receiver aur kush rf remote ir remote banata hu .electronics ke sath main last 12 year  se kam kar raha hu. last 1.5 year se main rc plane rc helli rc ouadrottor ki study kar raha hu .aur last kush dino se main rc india forum se juda hu aap old member ho es liye please mery es project me help karo
        thank you
        Ram singh
       

See Ashta's thread, it is one of the cheapest Quads around :

http://www.rcindia.org/self-designed-diy-and-college-projects/quad-using-arduino-and-wii-mp-and-nunchuck/