I generally set rates on a per-project basis, based on how long the project will take to complete. Setting a flat rate up front ensures that projects come in on budget without any surprises.
Wondering whether I'm the right writer for the job? Take my services for a "test drive" by hiring me to work on a piece of your project (e.g., a webpage of your website). That way, both of us can get a taste of what it's like working with each other before committing to a full project.