It'll probably cost you a tenner for the glass digitiser if you want the faff of seperating the LCD from the glass. Another £11 or so to buy a replacement LCD.
So it all depends on what the hassle/risk is worth to you.
Personally I'd pay someone £50 to fix it and let them take the risk of messing it up. But then it's an interesting project if you are that sort of mind.
Lastly, depending on how old it is, you may want to take it back to Apple and see what they will do. They replaced my son's iPod touch free when he dropped it and smashed the glass. Even if they don't offer you a free replacement, they will usually give you the option of a cheap refurb. If it's still too much then you can DIY.
£4.95 from amazon for the glass/digitiser and the tool kit. The video on YouTube looks fairly straight forward. I'm up for an upgrade in October, it's out of gaurantee so it's £146 for a replacement from apple or "a bit less" to have the screen replaced.