If you stay on one farm and don´t have any special needs you will only need travel expenses.
Train - you should book through internet well in advance = cheaper.
Swebus is cheaper.
Local transport sometimes want you to buy a card in advance, which is cheaper.
Hitchhiking is hard.
Food : Sweden is considered expensive. By in big supermarkets and avoid "restaurants" and expensive snacks.
If you need to stay over in certain towns, try couchsurfing.org.
If staying in hostels and eating on restaurants you can spend 350 skr or more a day.