Enables the transfer of a solute or solutes from one side of a membrane to the other according to the reaction: Folate derivative (out) + anion (in) = folate derivative (in) + anion (out). The Reduced Folate Carrier (RCF(SLC19A1) acts by an antiport mechanism. RCF carries several folate derivatives: MTX, PMX, ratitrexed, pralatrexate, 5-methyl THF, and 5-formyl THF.