und ‧ er ‧ charge /ˌʌndəˈtʃɑːdʒ $ ˌʌndərˈtʃɑːrdʒ/ BrE AmE verb [intransitive and transitive]
to charge too little or less than the correct amount of money for something OPP overcharge :
The city is grossly undercharging (=charging far too little) companies to use the land.
undercharge somebody by £1/$2 etc
They undercharged me by about $2.