http://ajsutton.co.uk for genuine Yam.
If you need a complete set of bearings, seals, and the sleeves the bearings run on (which will prob be knackered if the bearings are) then you are looking at about �230 in parts.
There's actually four sets of bearings if you count the ones in the swingarm at the other end of the dogbones.
Seven bearings, eight seals, four sleeves... adds up pretty quick.
You could almost certainly find the bearings and seals elsewhere, whether the potential saving justifies hours of searching to find them is up to you. The sleeves you will need to go to Yam anyway.