How much does a dirt bike tune up cost?

I have a 2002 Honda XR250R and it's never been tuned up. all that i did was change out the oil, from time to time, rode it once or twice a month to keep it from sitting to long and cleaned the chain and sprockets. Can anyone tell me how much a tune up is? and also how much is a valve job? or do you not think it needs the valves cleaned?How much does a dirt bike tune up cost?
700