Best way to get around London on a budget

While it has an expense, the combined transit system is the best. Combination of Bus, Underground, and trains. You can get an Oyster Card for a 5 Pound deposit, then add funds, it deducts the cost of the trips at a discount over single use tickets, plus if you are using buses or the tube a bunch in a day, it tops out at about $10, depending on what zones you are in. If you do a good job planning out your day and picking the right spot to stay, then you should be able to limit your trips to a couple a day, but I find it is more like 4 or 5 trips. At the end of your stay, you can redeem your Oyster card and be refunded the deposit and any unused funds.

As others has mentioned, get the Oyster card. Get the regular Oyster card (it's blue) rather than the visitor Oyster. I don't think there's any benefit to getting the visitor version and the 5 pound deposit for the regular card is refundable (I don't think the visitor card deposit is refundable). I have kept mine for years since I go to London every so often. The money on the card just sits there until you use it. If you don't plan to go back to London just get your deposit and remaining amount back from one of the booths. Hope that helps.

Thanks so much for your help. It's great. This info combined with vistacity.com helps us plan the trip..