Converting benzoic acid into meta-fluorobenzoic acid
Two steps should be enough ;-)


Nitrate benzoic acid. In J. Chem. Educ., 1967, 44, 464
(DOI), the authors added benzoic acid to fuming nitric acid at 0 °C. 3-nitrobenzoic acid is the major isomer (~ 75%). Recrystallize from ethanol. 


Your product is an electron-deficient arene and $\ce{-NO2}$ is a decent nucleofuge. Try to replace it by fluorine in a nucleophilic aromatic substitution!


In the case of 4-nitrobenzoic acid, the transformation to 4-fluorobenzoic acid has been described to work with a yield of >95% in a room temperature reaction using DMSO as a solvent and anhydrous tretrabutylammonium fluoride (TBAF) as the reagent. (DOI)