seems you need jEdit
It have the highlighting described, autobackup, and almost all of the features the expensive editors have. And it's totally free.
Needs some more memory because it is written in java (this should not make you sceptic!) it is not simply the best editor, but it the best programme ever written in java

You have to use some time to custumize it to suit your needs, but i can assure you it is possible to do whatever you want from it.