If you can get a bus to Margao from your start point, you can easily catch another bus to Mobor/Cavelossim (about 25/30 minutes by bus from Margao) The bus will take longer but will be cheap as chips. A fixed price taxi from the airport to Cavelossim is about the equivalent of £9 (or at least it was in April 2009). Google the Children Walking Tall website for guidance about taxi fares between different destinations. Haggle and bargain hard are, as ever, the order of the day....