An annual season ticket from Redhill to a destination that is Forest Hill, or Rotherhithe, or one of the stations between those two, is £2,220. Obviously, buying to Rotherhithe gives you most for your money. That is about £500 cheaper than an annual season from Redhill to London Bridge.
An annual travelcard from Redhill to Zones 2 to 6 is much the same price as the annual season from Redhill to London Bridge: it would require you to leave National Rail/London Underground in Zone 2, but would allow you to use buses into Zone 1.
An annual travelcard from Redhill to Zones 3 to 6 is £2,436. You could get as far as Honor Oak Park with that, but could then use a bus (e.g. the 63) into Zone 1. That would save about £300 compared with an annual season into London Bridge.