It will probably cost you about £100 to have the screen replaced by a professional repairer.
Personally, I would go for a professional repair with a guarantee, rather than buy a screen for about £10 and have the difficulty of replacing the item; which may Not function perfectly after a DIY job.
If you have Household Insurance it might cover such accidental damage. Check it out.
However,If you are courageous, there are lots of videos on YouTube which show how to replace a screen on your mobile phone. :-
https://www.youtube.com/results?search_query=Replacing+Screen+on+a+Samsung+Ace+3+
Hans.