You can plan a budget trip or luxurious trip based on your preference, but Gokarna could easily be a budget destination, if you are looking for one. Choose the stay and food and the mode of communication wisely as per your budget.
Travelling by bus would cost you 2k to and fro
train is cheaper one and can also enjoy when you go in groups. Stay would costs you 1k per night. You have Zostel in Gokarna.
Food/ Snacks would costs you within 2k for 4 days
To roam around you can hire a jeep or auto depending on size of group