Many Garellis had clutch issues. They would swell, and always engage. Make sure it can idle without the back wheel turning. This means the clutch is working. Put it up on the center stand, and give it lots of gas, so the back wheel is spining fast, then hit the rear brakes prety quickly. (dont slam on em) the engine should not die(stal) when the rear wheel stops.
I would pay $250 for a garelli in good condition.