It's not really sounding like the place for you! The DSM will have its own tourist vehicle on call, but if you wish to use one that you find based in Cavelossim, you will need a local sim card so you can phone him when you need picking up etc. Last year, it was taking about 4 days or so for a SIM card to be registered, but it may be quicker (or slower!) this year. The DSM will probably not be keen to phone the rival taxi for you.
There is quite a taxi cartel in that area and the taxi prices seem very similar, all overpriced in my view for shortish journeys, but that's just the way of the world and the overall costs balance out with the cheap restaurant prices.
If you like quiet shacks, you could always stay in a small guesthouse in Cavelossim and walk up to the Bamboo House up by the estuary everyday. They do lovely food, quite a bit of which is organically grown in their own grounds and they have loos!
And take the odd taxi from Cavelossim to DSM area for a day to experience the shack there and maybe have dinner at the DSM. But don't expect a bargain taxi in Cavelossim either!
Or, you could hire a scooter and have your own getaway vehicle at the ready for evenings out in the bright lights of Cavelossim (but do you want to drive along those zigzag roads in pitch black, without protective motorbike clothing, not to the mention the scooter driver having to miss out on a beer in the evening to keep the mind sharp for the drive back?)
It always looks like such a nice place though...