If you're just starting out, and not confident in your own modelling skills, then charging top dollar straight away is not a good plan. That estimate I gave you would be on the very low end of what a modeller could charge, but keeping in mind people in different markets can charge different amounts. For example, in the states, day rates are way higher than the UK and Europe. However, living costs are higher with expensive healthcare etc so it's justified.
In your case, charge what you feel comfortable with, but most importantly be clear about what you can and can't do from the start with your client. So long as you manage the expectations, and don't give them any unwanted surprises (it takes you 5 days when you thought it'd be 2 days, etc) then you should be OK. I agree with Vozz above, it's important to charge your worth and not undercharge, but first you must get professional skills up to speed. Once you know how good you are, and can demonstrate that to new clients, then you can bump up your rates and live the dream (assuming your dream is being a 3d freelance modeller guy).
Good luck with it, sounds like you'll have fun and learn a lot.