Have a look at
this kit on ebay, it's for a 3-door, but you can get 5-door kits too. Not expensive really & if you're going to the trouble of fitting central locking you may as well do it remote locking as well!
Wouldn't expect it to be too hard to fit, as long as you've got common sense & a bit of automotive know-how. I'd set aside a day to do it as all door cards have to come off & you don't want to rush it!