How and how much should I charge for a project?

[expertsystems]

Hi all,
I am being approached by a software firm for doing some freelancing work in PHP-MySql. I don't know how do I charge them. Can you guys help me in estimating that?
I am from India and have 4 years experience in PHP-MySql. Which is the best way to estimate the price? If it is hourly rate, how much rate should I quote? I don't know what are the rates for a person having four years experience.
If anybody from India can he suggest a rate in Indian Rupees?
Basically, I want to know the estimation techniques from Indian perspective.

Thanks for the help in advance

Thanks and Regards
Rahul