If you want to assume the role of DBA in your company you should be open about it. Doing things secretly is not a good way to gain the trust of your supervisor. Let them know you are interested in that position if it should become available. Let them know you are serious by gaining certifications if you want. You might also consider working with the current DBA to learn the ropes and demonstrate that you are willing and able to do the work. Also, you might be careful about asking for a raise in salary that large. That is almost a 33% increase. That is likely to burst any budget.

It seems to me that your desire is not for the position but is all about the money. To be honest, I think with only 3 years of experience you are getting a more than fair salary. I would have a hard time paying somebody who is still pretty fresh out of school that much. Remember that your career should be a process, not a destination.