Only 4 days to go huh......
Calm down - lol - they're not that rare.
In the UK we pay £44 for a Fluval 104 new. Off the top of my head that's around $65. For a second hand one I wouldn't go over $40. With a new filter you'd get the proper medium, not just the stuff that guys trying to get rid of, as well as all the fittings that go with it, and not what he doesn't want any more, together with a guarantee etc etc - and the kit will be new.
Second hand you save yourself 20 bucks and suffer what ever comes out of the box.
I looked at the 104 this week - and decided to go for (another) 204 for the extra £6
'sup to you.........
