Because you are new to charging, you really have 2 potential strategies.
Strategy 1: Find out their budget, match whatever it is and do everything you possibly can to over-deliver. If you do a great job, it will show and you will know that doing this as a business is a good fit for you. After you get a rhythm for working with clients, find out exactly what competitors (of similar skill) are charging and use that number to pitch to other, new clients. You now have clients to prove your track record and can start to grow as a real business and raise your prices as you grow.
Strategy 2: Figure out what you think your time is worth based on your skills and location, then determine how many hours per week you really need to do the work required for them. You can then put together a package that ensures you are paid fairly for the scope of work you present to them.
There are pros and cons to each. Use pricing strategy 1 if you think this could be a real career for you and strategy 2 if you just think freelancing could be a nice supplement to your income.