it can be cheap to replace, it could be expensive. It depends essentially on the screen and your confidence in doing it yourself.
I broke the screen on my 17.3" HP (DV7 3112sa) Laptop and a replacement screen from eBay was £45 with free P&P. I fitted it myself in about 5 minutes.
My girlfriend broke her 13.3" ASUS (UX303L) laptop screen a few months back and a replacement from ebay was £90 with free postage... I ordered it and fitted it and it still didn't work, reset BIOS & still nothing, my computer engineer mate also did all he could and it didn't work so i sent the screen back and got a refund and got in touch with ASUS who wanted £205 to fix the problem (undiagnosed by them, i just said the screen was broke) and a local computer shop (propergeeks on Leasowe Road) wanted £170 and also said the motherboard was goosed and it had video card issues, which i know was a lie because if the laptop was plugged into our tv through HDMI it worked perfectly, same through a VGA monitor... we ended up actually just selling that laptop as parts (got a couple of hundred quid for it on the 'Bay) and buying another brand new working laptop as she's a freelance journo and needs a working screen and we/she couldn't deal with having to send it away or whatever.
so while underneath everything, as Mark says, they're all essentially the same, some are more difficult than others to fix so one option would be spend a little more and just get a brand new laptop [you can buy the ASUS X551CA for £175 with free P&P from HERE
(<- clickable link)