I know this is an old topic.
But I just changed the screen on my S740 (only the glass was broken). I ordered a screen from ebay including tools for 26 EUR.
I followed the instructions on this blog:
It's not the easiest thing to do because you basically have to take the whole phone apart, but it's cheaper than a used phone of ebay (plus you don't have to reinstall).
Device History: Xperia Mini Pro, X10 Mini Pro, Rose, Touch Pro, Vox, TyTn, Wizard, MPX200