You can get ample prepaid taxis from Madgaon junction. It will be quite expensive compared to the fare for similar distance in any other state. But there is little other choice apart from taking a unreliable public bus. South Goa's famous Palolem beach is around 35 kms from MAO, so expect a one way fare of 1200-1500 at the lower side. If one hails a cab from the road, he will charge a similar amount - especially if the destination is one of the tourist properties.