ZX9R Gearbox Problems

Hi all, newbie here. I seeking some advice. I am an older rider and have a 97' ZX9R. with 50,000 klms. The Drive sprocket (I don't know the technical term) has a degree of movement in it when changing gears. It seems to have a half turn of slip before a clunk stops it and it engages. This is apparent in all gears, also the box is very clunky through changes and is impossible to get into neutral when you pull up at the lights in first gear. Motor runs like silk and everything else is great. My question is - Is a rebuild in order or can a new box be sourced. What would one expect to pay for such repairs. I live in Cairns and do not wish to be ripped off by someone with a lot more knowledge than me (which is about everybody). Look forward to any advice forthcoming. Thanks