I think our very own Chris at Boxer Metal (screen name "bmweuro") has the best price on Hoskes. I think they're right around $380, if I recall correctly. I went el cheapo route and got some imitation Dunstalls for $55 per side. If I decide I don't like them, I'm definitely going to buy some Hoskes from Chris. I have an R60/5, and I found this YouTube video of what they would sound like on my bike. Very, very nice indeed. It sounds a lot meaner than I thought a 600cc BMW boxer could!
http://www.youtube.com/watch?v=sYzrZ4tFI5c
Good luck!