I saw some S520 print heads, they are the same for the S600 on EBay for $40
when I was looking, they were customer returns, not as good a price as
Michael found though. I had an S600 print head go bad 2 weeks ago also. Mine
would blink yellow 7 times which means a bad print head. I found that I
could remove it and rub on the top of the ribbon connector where it connects
to the green printed circuit board and it would work for a few weeks before
the same problem. They it would not fix again. There must be a connection
that goes bad on the ribbon cable. I have seen several people with bad S600,
S520 print heads.
Anyway I decided to get a new printer. I got the I560 for $90 which uses the
same ink cartages and has a redesigned print head. Way faster and better
with photos.