Many schools / programs only offer a two year Radiolog Tech program as an associates. Some schools will offer it as a bachelors. There really is no difference in pay at the tech level however having a bachelors opens you up to going into management or teaching down the road.
My advice would be just get the two year associates degree in Radiology and try to get your employer to pay for you to go back and get your bachelors.
The highest paying Radiology position is Radiologist which is a medical doctor with a bachelors degree, a medical degree, and 5 years of residency.