Olof Lagerkvist wrote:
... you would be able to reduce your costs by
avoiding travelling through Zone 1.

Possible routes would be:

East Croydon - Clapham Junction - Vauxhall - Brixton
East Croydon - Balham - Stockwell - Brixton
East Croydon - Herne Hill - Brixton (not many trains on these routes)
East Croydon - Beckenham Junction (Tramlink) - Brixton

This would enable you to travel on a Z2-6 Peak One Day Travelcard at
£7.40 per day.

The TfL Journeyplanner also shows an alternative route of train E.
Croydon - Tulse Hill and then bus 2 or 432 to Brixton. It estimates this
journey time 00:36 so if it is correct it would not take longer time
than train/tube via Victoria. With this train-bus route a Z3-5 7-day
travelcard will save some more money because it costs £18.40. Divided by
3 days that is about £6.13 a day. Then, a few pounds more can be saved
by buying monthly or longer travelcards.

Olof, thanks for all your suggestions - I will try these out to see which
suits best.

Regards,

Demiurge.