I am new to Game development and planning to make a multiplayer turn based card game, the server should be authoritative so no players can cheat. I checked few BaaS solutions like PlayFab, GameSparks and HeroicLabs but there is a pricing concern and not clear on how to choose the service. Please suggest some networking solutions for my game and how to choose the best one.

What are you used to developing in?

For a card game, a server in node.js, using websockets for communication, could be perfectly adequate. It also lets you easily support web browsers as clients. Probably want to use TypeScript rather than JavaScript if you can help it, though. You can host one of these for free for a year on the Amazon AWS free tier.

Another option is FireBase. It's mainly aimed towards mobile and web games, but has a generous “free tier.” They have a Unity SDK: https://firebase.google.com/docs/unity/setup