From Purfleet train to Rainham then line 103 bus to Romford Station. 36 min £6. From Dartford taxi to Romford. 23 min £76. From Dartford drive to Romford. 23 min £3. From Dartford walk to Romford. 5 h 52 min.
There is no direct connection from Dartford to Romford. However, you can take the train to Rainham then take the line 103 bus to Romford Station. Alternatively, you can travel from Dartford to Romford in around 23 min.