IIRC it cost my mother £100 to do hers. It cost her the same about five months back to basically change it so that every penny goes to my brother. Couple of reasons, really. 1. If I get my hands on £140k+ it will be gone within a week, so my brother will be getting it all and then buying me a suitable flat that I can live in forever without having to worry about being evicted and... 2. My ex is still my wife (worse luck) and if my mother died before we are fully divorced.... Yeah, not something I would even want to contemplate. Every time I think about my mother scrubbing floors and working 7 days a week to pay off her mortgage it makes me feel quite sick to think my ex could get her hands on even 10p of it.
@Kronos, You could just hand over all your worldly belongings to your other half now and save a load of trouble, I'm sure she won't mind.
!. Don't do a will online 2. Name people who do/don't get benefits - to be sure leave a token amount such as £5 to anyone who may have even an oblique claim on the estate you may leave behind. 3. If you do a pre-packaged will - make sure it gets witnessed properly.