Snowspeeders are one of the few items that haven't really changed much in value since the late 90's. Reckon around £75 at most. These were going for £200+ on certain stalls at Celebration.
Pink Palitoy generally seems to be a premium over the blue Kenner version, but I would only put it around the £60-£70.
I'm basing that on not seeing any instructions or harpoon block and original string...