Hi VK,
there are some affordable hostels are:
1. Pappi Chulo, Vagator
2. Jungle by The Hostel Crowd, Vagator
3. Bunkin Hostel, Calangute
4. The Hosteller Goa, Anjuna must do-activites in goa are:
1. Beach Hopping:
2. Visit the Chapora Fort:
3.Enjoy the Night Markets:
4. Visit the Spice Plantations: If you want to know about more details about goa visit the website Backpackers United https://backpackersunited.in/