I may be completely way off, so dont take my word for it. I have a GO 737-300 Fibreglass model, and its worth (brand new) approx £75. My guess is yours is probably approx £125, maybe more. Purely because it is quite big, its fibreglass and it has a perspex base. Use Ebay if you want to sell it, I often see large models like the one you have described on there, and do a search for similar models on Ebay to see the prices they are going for. (Because my advice is so great I can offer you £10 for it!! Good deal!)
Let me know if you are selling it on Ebay though, I wont bid but Id like to see what it sells for.