But how much I can score hourly as mobile developer there? Any clue?
Also how much of the projects there are real? And how hard is to get projects?
Your hourly rate very much depends upon your skills. Start bidding high, and see if you get any catches. There are people on these sites making $100 / hr., but these people have a lot of history and are well-known. Don't expect to make the higher rates when you're just starting out, and remember you're often bidding against people in third-world countries. At the same time, remember that you'll be taxed as self-employed, so make sure your rate includes the amount you're likely to pay in taxes in your country, and make sure you save that percentage back since you're likely going to owe big time when you file your income tax.
Getting projects is a challenge; mostly it's about projecting a professional appearance through your proposals. Make sure your English and grammar are top notch. Justify why you are the best person for the job. Tell the employer what you'll do to build their project. Split the project into milestones (each with payment attached). Essentially you should be writing a highly customized cover letter in every proposal.
Also, not sure what country you are in, but for many Web design and simple programming jobs it is hard to compete with those willing to do the work for a much lower price (I even saw some people bidding for jobs at $2 per hour in some cases).
Just my take.
Also, I don't do web. For mobile I use cross platforms SDK or native.
It was my source of money when i was a student (it used to be getafreelancer.com)