Will you get high school credit for the class? If you are hoping to get school credit, you may be limited in where or how you can spend the money and take the course. If that’s your situation, you could talk to administration at your school, though it sounds like they may not have many suggestion, but at least you can make sure the class you end up signing up for follows any possible restrictions your school may set.
If you aren’t taking the class for high school credit, you have a lot more leeway in the types and locations of classes you can take. John’s Hopkins in a good option if you are looking for guided online classes, however you usually have to take a test to qualify for the program, and a qualifying score for the specific class you are interested in. Additionally, it sounds like they don’t have the science classes you are looking for.
What science classes have you already taken in high school? If you have already taken AP science classes in an area of interest, you might be prepared to take a college science class at a local community college. At my school, they offer dual enrollment to allow me to enroll in a couple classes, but you would have to work out the specifics with your school. In that same vein, online sites like Coursera or edX allow people to sign up for classes sponsored by college professors at all sorts of schools in a huge variety of topics, including many on science subjects.
Finally, if you aren’t hoping to get any credit but just looking for enrichment, you could buy a textbook for a subject that is really appealing to you and use the rest of the money to get a tutor to help you through it (or don’t get a tutor, that’s up to you).
I think if you could let us know how you’ve done in the classes you’ve taken and a little more insight into your interests, we might be able to help more.