I have an interview tomorrow and this would be very timely. How do I ask for a higher pay without being too rude or sounding like I am?

Ask if it's premature to discuss remuneration at this point in time

Bear in mind that it's considered the employment market currently and unless you know what's the salary range offered, putting a figure that's beyond a company's pay ability might remove you from the race so be very careful on how you broach the topic on salary. Certain factors are intangible in terms of the value that it would create for your career like getting yourself hired where you will then acquire the much needed experience that would enhance your future employability. Entrust the salary to be offered to the company because if they are serious about you as a candidate, they will treat you with respect by offering a salary that's competitive, fair and equitable based on your profile.