Service intervals are 6000 miles for your 2004 model RSVR, alternating between a minor and major service. A minor service should be in the region of £150 which is a basic oil and filter change, levels check, lube etc.... A major service includes a valve clearance check and would be around £350 to £370 at an Aprilia dealer. Also spark plugs and air filter are changed on this service too
Where abouts are you. If you're not too far from Tamworth, midlands, then pm Griff aka fusebox, the meister on all things Aprilia as he runs Custom Resto and Race and will gladly service and fettle your bike. He'll be lurking about on here somewhere