I can only tell you of my experiences. If you start in informatics in the hospital where you are currently employed as a nurse you will likely be starting at a base nursing salary (without shift differentials, weekend differentials, etc.) and usually the position will be salarlied not hourly so there will be no over time. You can always try to negotiate if you feel you have some special knowledge, skill, etc. but typically nurses who enter the informatics field are payed at a higher rate than others who enter strictly as analysts, etc. because you are being hired for your nursing knowledge.
If you leave your hospital environement to work with a vendor you may actually be able to negotiate a higher salary, but if you have no experience in informatics you may still be making the kind of salary you would if you were a working in the hospital. You have to consider that it takes time to learn and for your employer to train you and for you to become a productive member of your team.
Once you gain experience and knowledge and prove yourself you are in a position to command a higher salary and you are more marketable. You can check out other employers or even start your own company.
Getting started is kind of scary, but it's a rewarding field with ever expanding opportunities. BUT you have to be interested. You have to have certain kinds of skills - ability to analyze; ability to step out of your comfort zone from time to time; ability to work as a team, but also work independently. . .
One more word of advice if you are a nurse looking to move into Informatics - make sure you have at least 3-5 years of solid nursing experience. It's your knowledge of nursing and medical procedures, work flows, policies, etc. that make you most marketable.