Upvote:2
Generally the London Oyster daily cap only applies to any destination/stations within Zones 1-9. Both Stansted and Luton airports are outside of this area so in order to get there, you would have to pay another fare after leaving the Oyster zone.
I would recommend Easybus to get to Luton/Stansted cheaply http://www.easybus.com/en/
The full map of where you can use a contactless card/oyster payment is here: (Includes Heathrow and Gatwick airports)
Upvote:5
Looking at my handy zone map, I see that Tottenham Hale (TOM) is zone 3. A quick look at a selection of trains from LST to SSD shows that all stop at TOM but next after that variously at Harlow Town and Bishops Stortford, both of which are well outside the capping zone (even Cheshunt is zone 8). So I don't think you can do better than to use capped Oyster to TOM, then travel by ticket to SSD.
However, even with National Rail services, the rules about combining tickets are that you must use a train that stops at the place where you go from one ticket to another. In the case of Oyster, it's even more onerous: you'll have to physically disembark in order to tap out.
I note that an Anytime Single from LST to SSD is £18.10, while one from TOM to SSD is £16.70, a difference of £1.40; less if you're using an off-peak ticket. Whether it's worth getting all that luggage off the train, finding an Oyster tap-point, possibly changing platforms, and waiting for another train in order to save £1.40 is a decision only you can make. I certainly wouldn't bother.