you can have it fixed for 62.50€ on ebay
i am not sure if you can find a original screen on ebay but i would dig a bit for that because it might turn out to be cheaper.

i would suggest you to buy a used N900 (maybe between 100 -150€) and keep the broken one. if for example the usb port will break you can swap spare parts. or look for a defective n900. i bought a "faulty" n900 for 73€ (incl. shipping) and after reflashing it once it works perfectly

edit: did not see your post that you already have new screen.