You can book a cab easily and I guess it would helo you out.
However, I would suggest you to visit Goa and then book a tour as it would help you in negotiating the price.
Face to face negotiations are much better compared through an email. Note: there are lots of tour agencies. So finding them is not at all hard.
Plus to book a cab you may also use Goa Miles run by Goa Government. A nice initiative by Goa tourim. You can download it for Google Play and IOS. as well.