Before you go back to school, it's always important to determine exactly what your financial commitments will be. How much will your books, tuition, commuting costs, and other expenses total up to every semester.
With online education, many of these expenses are nonexistent. For example, rarely if ever will you need to commute anywhere. And some programs don't even use textbooks. All of the material is online. Not to mention that expenses such as room and board are nonexistent since you will already be living at home. But even still, the costs can get up there depending on what type of degree you want to pursue.
Before you can determine how much an online degree costs, it's important to establish what discipline and what type degree you want to pursue. For example, a two-year associate's degree in English will cost much less than a six-year Ph.D. degree in astrophysics. As a general rule, the longer the program, and the more specific the discipline, the higher the online degree costs.
Again, this is a very difficult question to answer, because it really depends on what track you want to take. But online degrees tend to be significantly cheaper than traditional campus degrees. That's because online degree programs can accept a lot more students, and they have a lot less overhead. These extra savings can be passed on to you as a result.
It's also important to point out that many people who are pursuing online education are doing so while holding down a full-time job. In many cases, your company will sponsor some or all of your online degree tuition costs. Talk to your supervisor about making some type of arrangement.