Going through my 'bits' box the other day I found an incomplete set of Ernie Ball flats that I put on my 5 a while ago and then took off a couple of months later.
They are a .045" set, but the D is missing. Also the 'G' is cut for a 4 over 1 configuration, so it won't fit on a fender style bass.
I've got the B, E, A (which will fit a fender style headstock) and a G which won't.
They were £50 new last year, so I reckon £5 per string isn't unreasonable, I'll cover postage.