I found the probate process incredibly easy to deal with and the people at the Probate Registry exceptionally helpful. (So much so, in fact, that I nominated them for a Charter Mark, resulting in me receiving a really nice letter from them in response).
So, like NewJudge, I'm confused as to why completing form PA1 should be giving you problems (it's far, far simpler than most 'official' forms, such as the ones for applying for Job Seeker's Allowance or Pension Credit) and bewildered as to where a figure of £4k comes from.