I'm sure price ranges can vary, but in my case I was quite comfortable paying $150/hr. If you look at a few web presentations from the Fee Only folks, look for a link to "Getting Started" which will guide you as to how the transaction will look. If you decide to use him/her, they will construct a "statement of work/ project scope". Mine had a checklist of things to select from-things I wanted (portfolio review, SS and pension claiming strategies) and things I am not interested in spending money on at this time- (insurance review, long term care alternatives, estate planning)
My guy was not a "clock watcher" by any stretch of the imagination and at the end of our 90 minute "1 hour assessment" meeting, he was able to verbally give me a project plan, with a capped cost (...no greater than without further approval). By the time I got home, he had PDF contracts waiting for me to sign.
The process for me was to gather up everything on his checklist- statements, SS projections, pension papers, spreadsheet listing assets- and deliver them to him with a signed service agreement, and 50% up front/balance due upon completion.
For me, I consider myself organized and financially astute...but I still didn't know what I didn't know. I believe I have mapped out a financial road for my wife and I through late retirement, but I wanted to put some guardrails on that road.
FWIW, if you are considering a MMM style FIRE scenario, I would very early on tell the advisor that in the initial interview and see if they look at you like you have 2 heads- as we know from these forums, not everybody can grasp a 20 year career supporting a 40 year retirement guide path. I had a commission driven FA look at me as if I were nuts for having retired at 57- "What are your objectives?" he asked "My objective is to never hand out another business card in my life" was my answer. I told him I was using a fee only advisor and he asked "So this guy is going to give you a plan for about a thousand bucks?!?" I said "...A little less" He said "I can't make any money like that!"...to which I nodded and said "Correct".