Most instant coffee is... well, it's better than NO coffee. Starbucks make these little packets of instant coffee which contain micro-ground coffee, so it's sorta instant plus "cowboy coffee", and it's strong.

According to the Mayo Clinic's website:

                                            Caffeine 
  Generic brewed              8 oz. (240 mL)   95-200 mg
  Generic instant             8 oz. (240 mL)   27-173 mg
  Black tea                   8 oz. (240 mL)   14-61 mg