The cost of a full-day taxi fare in Goa can vary greatly depending on the specific service you choose, the time of year, and the distance you plan to travel. Some taxi companies may have fixed fare for a full-day tour package, which includes various places to visit. It's generally recommended to negotiate the price with the driver before starting your trip, or you can contact a taxi company that provides this service and check the fare with them.

The fare may also depend on the type of taxi you choose such as Sedan or SUV which will have different price per km or per hour. The price also varies during the peak tourist season and off-season. Some taxi companies may offer special deals or discounts for long-distance trips or for booking in advance.

It's a good idea to research different taxi services and compare prices before booking your trip. And also to check the reviews of the company before hiring the taxi. This will help you find a reliable service that fits within your budget.

It's also a good idea to ask locals or other tourists for recommendations on reputable taxi services in Goa. They may have personal experiences they can share with you.

I hope this information is helpful. If you have any further questions, feel free to ask.