Nut Files what to buy?

[Phil Starr]

I want to bring the string height down a little on some of my basses. I'm looking at nut files and they seem to be either less than £10 or over £200 with little in between. There are also some sets of two or three with plastic handles  labelled  sizes 3-5 without saying what 3-5 actually means in mm or inches. There are also setsof needle files for general purpose use but I already have sets of these, and I've seen people wrapping old strings in sandpaper and using that as a tool. 

 

It's Christmas and peopleare asking what to buy me. There's nething I really want but if I could find something that would make the job easier then files in the £20-30 range would be a great present I'd actually use. I hate the idea of people wasting money on something I wouldn't use. Any suggstions?