Throwing it out there because our FLR(M) re-applys are relatively close– mine is April 2020, hoping to slide in before the fees go up that year. I'm budgeting about £3,000-ish for my 2nd round. I also have to renew my passport and a couple other things before my application. Really based on all the figures that KFdancer brought up.
I'm also hoping to do the in-person service because my job means I travel fairly frequently and need an ID on me. Can't really afford to not have my passport for extended periods of time. Will mean I'll need to save a bit more.
However, doing the mail-in service will save you quite a bit; and if you can be without your passport for a bit, I'd recommend going that route TBH.