it is possible to do it yourself. Tghere are 2 types - property and affairs (money) and personal welfare (health decisions) you can download the forms from the office of the public guardian website, and they cost £150 to register (each) although i have a feeling that price has changed recently.
You also might need to pay a professional to certify that he has capacity
as a rough (Ish) guide me and husband did them at the solicitors (so four in total) plus a mirror will and it cost us roughly £800 altogether. This DIDN'T include registering them (they are not currently registered) but did includ ethe certification by the solicitor that we weren't acting under duress and that we were who we said we were and also includes storage at the solicitors office Whenever i put this price on here i get loads of peeps telling me i was ripped off, but i feel safe that they are done properly