Is there a legit way to travel in India with no expense? Some legit ways? Like is volunteering legit? And how can I do it?

Commit some deadly crime, police will give you free trips to different places. Kidding.. you can opt for volunteering in some exchange program or local NGOs have their field visits often.

hitchhiking is the only way, few options for staying for free are gurudwaras, couchsurfing is there but not much scene in india, try reddit solotravel_india, you can get some options from there if you would describe what's your plan.