I'm afraid its a scrappy job. A new 'box or a recon box would be costing something like £700-1200 (recon. vs. new).
Scrappies would charge about £50 (I got a 6speeder for £45, but forgot to get new fangled linkages, as I run a 5speed as std) and maybe a tenner for getting it out for you.
A good garage would charge £45-50 for new clutch parts (get it done whilst the gearbox is out of the car otherwise you are wasting your time) and about £100 for labour.
So all up you are looking £200-250 for a good job. theres no gurentee that that box would be fine but they are generally pretty sound.