I studied for my MSc in the UK mid-career. I didn't really do it for the potential payrise (there is/was none), I just did it because I enjoy learning about computing and wanted to do something structured so that I stuck with it. It cost me about £10,000 and I paid monthly over the 2 years so it wasn't so bad financially. I think you can take a loan in the UK to cover postgrad stuff, but I didn't bother, I was in the fortunate position that I could afford not to.