Shifting 2nd --> 3rd == CLUNK...

My manual 89 DX is generally a solid car, with about 143k miles on it, and I expect that the clutch will have to be replaced pretty soon, but as it stands now, whenever I shift from second to third gear, there's this mechanical 'clunk' of sorts, it almost feels like something's about to hit the floor of the car.

Now, I got this thing for $500, so I expect problems. My last car's engine went before I ran into any clutch issues, and after that I bought a new car. So I was wondering if anyone here has run into a similar experience and knows what I might expect to have to deal with here.

Thanks :)