However markedly does it take to fix an Acer Aspire 4920 laptop keyboard?

So right. I accidentally, NOT CONNECTED PURPOSE, broke my friend's upright. I threw a book at my colleague and it fell on her keyboard and 3 keys fell out. According to one of my friends, you need to change the whole keyboard. Its an Acer Endeavour 4920 laptop. How much do you think that would cost?