I have no experience of either as a monoshock (my old race bike originally had Hagons on when I bought it though) but you can get the YSS one new (presuming the one you have been offered is second hand) for only a little more:
http://www.wemoto.com/bikes/ducati/m...ies_monoshock/
One thing that I have noticed though is that the YSS one has holes in the pre-load adjusting ring meaning that with the very limited access to the top of the shock when fitted makes adjustment a lot easier than a 'C' spanner which the Hagon uses.
Also the Hagon has a stainless body and the YSS looks to be anodised Aluminium so I guess you pays ya money and takes ya choices.
The Hagon option:
https://www.hagon-shocks.co.uk/catal...?partno=M60033
I know you're on a budget but I really can't recommend Nitron shocks enough- I've had mine on my 900 for eleven years now and it looks as good as new after having it serviced- they even corrected a little design fault and fitted a new top free of charge so their customer service is about as good as it gets too. They'll even fit a black spring if you don't like their trademark turquoise.
Worth thinking about at least:
http://www.nitron.co.uk/catalogue_it...9&prodID=73975
Before the service:
Measuring Pre-Load:
Fully serviced and looking new after eleven years: