I have recently made a couple of nuts myself from bone blanks and did not find it to hard. Like most things quite a bit of patience is needed and it can be annoying if you get it done then realise its wrong.
If the nut you have at the moment is the right heights etc, you have a ready made template to use and are half way there.
When I made mine I decided that buying files was not worth the money as a set does not come cheaply, instead I cut the slots with a very fine saw to just above the height I wanted then used the wound strings from my acoustic which were 1 size up from my usual electric gauge (11s) to widen the slots and sand down the last little bit, on the 2 lightest strings I used some folded some fine sand paper to fine the slots. I have done 4 nuts now the first I had to throw away as I got the slot angle wrong and rounded over the slot on the fret board side which would have messed up intonation, but the other 3 have been great.
If you have the time and like making stuff I would give it ago yourself at worst all you will 1 or 2 pounds buying the bone blank, you can always put the old nut back if it goes wrong till you can get a replacement or take it to a tech. If you get it right you have a bit of your own blood, sweat and soul helping you the music you want.
