If you want a job that will pay better, keep you in a higher education environment and then possibly pay for your nursing school....then you need to get employed inside a hospital. That is absolutely the #1 way to get a free ride to nursing school. Some hospitals advertise this fact and others keep it quiet unless you ask, but if you were to be a star employee in your role and then ask after 1-2 years for tuition assistance provided you sign an employment agreement in exchange, many hospitals have and provide this ability as they do like "growing their own".
As an EMT-B, you will not have much luck getting inside a hospital as an ER tech. It is possible but not a sure thing. The role you are most qualified for would be patient transporter. Not a glamorous job, however it is important and it is step 1 to the long term goal.
If you think that is not your cup of tea, then get a phlebotomy certificate and an EKG tech course. A lot of tech schools offer those as a combined package. If you have to choose ONE, then I would push you towards EKG Tech. Once you complete this class, you are now able to sit in front a bunch of monitors for 12 hours at a time watching rhythms. Hospitals always need EKG techs and the roles vary within each place. You might run room to room doing EKGs or you might just be the monitor tech. Either way, it is a good job, pay is ok and again it is getting you closer to that end goal.
Getting inside the hospital is going to expand both your knowledge and your vocabulary if you just listen. Stay focused on end goal, do the job and then follow through with the steps necessary to achieve the end goal.