I had one of the old DR600, compleate with rear drum brake for 16 years. Standard it was an absolute pig to start but I loved it dearly. I took the motor out and left it with TTS near Silverstone and got it back after it had been gas flowed, head skimmed, barrel skimmed (don't ask!!) and re-cammed. I had many weeks after playing with jets and airbox mods. The end result was by far the best bike I have ever owned. I toured thrashed and generally hooted around for the best part of 38,000 miles post rebuild and it is still going with its new owner. It was also unbelieveably easy to start after it had been altered
In standard trim it was set up with very weak jetting to get it through the regs and it was very difficult to get lit up once warm and would kick back very violently if you got it wrong. There was a knack to it for sure (standard and modded). So a tuned the DR650 could be a good buy. I used clutch plates and chains and sprockets but that was it so spares might not be a problem as long as you don't have a Biggy. It was 100% reliable. DR 650's are sooo cheap right now, I'd buy one and make it really evil.