It might be expensive through a solicitor, but it will be worth it in the long run. I've had to go through the process 3 times - once to do my own, but also for both my parents (both deceased now) and also for a (now) 98 yo aunt who has no children. I've been her EPA (we call it Enduring power of attorney) now for about 10 years, since her stroke, and I have been able to handle all her affairs (like bill paying, banking, selling her house etc) which has been a godsend for her. If it gets to the point where your father isn't capable of making his own decisions (ie dementia), and you don't have an EPA, it will make things really difficult because you won't have any authority over his affairs or finances, and the courts will have to get involved.
I'm not sure how is works in the UK, but in Australia the EPA also has to be registered with the government to be fully authorised, which could be an additional fee that you might need to take into account, unless of course that is included in the solicitor's fee. However, you would have to see proof that the fee is being paid to the government (if that's the case in the UK).