Hi - I work as a fee-only planner at an RIA and I sat for the CFP exam last year, just working on the experience portion in order to officially be a CFP. [In order to use the title, you need 3 years of experience in the field, or 2 years working under /being vouched for by someone who is a CFP, in addition to passing the exam and a few other things.]
In almost all cases, you need to complete a financial planning education component in order to eligible to sit for the CFP. I did the cheapest online self-paced option I could find (Bryant University online) and that was $2,490. So, it's pretty expensive if it's just something you want to do for fun. The test itself is not that hard if you're a smart, technically-inclined person who is good with academics. (I can't call a test hard since it's straightforward exactly what you need to study, such that if you put in the time, you will pass assuming you're a reasonably intelligent person.)
I would recommend looking into the Enrolled Agent designation (which I recently completed) - 3 parts of the test, which you could take all in one go if you want, much cheaper to buy the materials. Part 1 is all about individual tax returns - super interesting to know and apply to yourself.
Ultimately, I don't think it makes sense to go through the CFP education/certification unless you're also working in the field. It's costly and you'll have to go through material that isn't at all useful or interesting to your specific situation.
I absolutely love my job now. (Previously, I studied econ/math in undergrad, worked in consulting, and got a master's in finance from an Ivy by dropping out of a PhD program.) The fee-only planning world is quite small. You might try looking up advisors in your area (via NAPFA or Garrett Planning Network or XYPN) and seeing if anyone's willing to be taken out for coffee, to tell their story. That would probably provide you with good insight into the field.