Is the clutch sliding already? If clamping power is fine, it might simply be the clutch lnkages that need servicing.

If its a cable-type clutch, you might need to replace the cable already or grease the cable.

If is a hydraulic assist type clutch, you might need to drain the old clutch fluid and replace it with new fluid. The clutch master cylinder might also have leaks / bubbles so you might need a repair kit for this as well.

Fluid costs about 500 per liter for the nice brands. The clutch cylinder repair kit costs about 1,000-1,500.