I'm a 20 year old student studying Graphic Design. I occasionally get clients who would like me to completely redo their website such as designing a custom theme, adding plugins and doing it all with wordpress.
I agree with Dan. The hard part right now will be estimating the time, so I suggest padding your estimate by 20-25% to account for that. If/when you come in under budget, your client will be pleased.
Be sure to use a contract so both sides are in agreement on what the project entails. And if a client balks at signing anything, avoid them. I suggest using Contract Killer 3 as a template for the contract. It helps make clear, in plain English, what the project expectations are, what happens if someone changes their mind and covers legal obligations.
Lastly, don't work for free or less for 'exposure' unless it's a non-profit you care about. Your time has value and most 'exposure' will not return a commensurate value unless it happens to be an incredibly high profile website (in which case they'll be able to afford you).