A set of tires for a B6 should come in ~$200 +/- depending on brand and where you buy them.
At 6000 miles the only service, besides a few oil changes, should have been a valve adjustment and torque check of everything in sight at 600 miles. Many dealers will skip the initial valve adjustment, but that's what the book says.
Your next service is supposed to be at 7500 miles and will include everything a 600 mile service did.
Nothing special to look for that you shouldn't look for in any used bike. These things are normally reliable and well built.