I've got an 04 that I bought new and has about 23K miles. It has been a great bike. It has a comfortable seating position, but still takes the curves well. I've upgraded the fuel lines and quick disconnects. An aftermarket seat was a good improvement. Except for that, it is stock. I've never had a problem. It's got a nearly bullet proof engine and transmission. Overall quality is very good. The brakes and suspension are fantastic. The suspension can be improved still with aftermarket shocks. I'll get those when the stockers are worn out.
I've done the maintenance myself, it is pretty easy and not expensive at all. If the bike does not have ABS, then I would say the maintenance is very easy.
As was mentioned, the clutch and FD have failed some owners. Those topics are always beat to death when they appear on the discussion boards... especially the clutch spline issue. The FD bearing failure can be usually be caught early, and it is not as costly as the clutch spline problem.
I think it's fair for clutch spline victims, who bought their bikes new, to be upset with BMW. They should be, as the bike came from the factory with that issue (all models of oilheads suffer from this, not just the R1150R's). They got faulty bikes that don't reveal themselves until (typically) the warranty has expired. I think BMW is really doing themselves a disservice, by not helping those folks out. Those people who bought the bike new, paid A LOT MORE than you are looking at spending... keep that in mind.
To be completely honest, I have some worries about this myself. I will open my bike up and inspect the splines. I am generally not a lucky individual... so I am probably more worried than I should be. After my worries are laid to rest, I expect to keep the bike for a long time... fingers crossed.
Besides that one issue
which only a small percentage of people have suffered, I think it's a great bike. It's not perfect, but I have never expected that of anything. It is what I want in a bike. From normal daily road riding, fast and twisty joy rides, to light touring it does everything for me, very well. It is as tight and fun as the day I bought it.
At the price you are looking at... I think you may get a great bike... that has a ton of miles left in it... at an amazing price.
Get those service records if you can.
I was dreaming when I wrote this, forgive me if it goes astray...