More skilled workers are going to command a higher wage.
If you increase your offer then you will have a better chance of finding someone capable of doing what you need done, especially considering that you are looking for a native English speaker.
You are free to offer however much you wish, however I would suggest offering between $40 and $60 for four hours of work.
I know it's not much, but I can't really afford to offer much more. I'm still a student, and starting a website is already quite expansive, because of the domain, hosting and SSL certificate that I decided to take. I mean, I started this website during my free time as a challenge, and I've already invested more than I expected to. If the website really takes off, I will of course reconsider this position but in the mean time, I'm just looking someone speaking correctly and able to correct the majority of my mistakes, to make the website look a bit more profesional.
Thanks for the offer, but I've already had several answers from other users. I'll stay in touch with you if I ever need your help later down the road.