"I've been raised that, generally speaking, if someone invites me somewhere, they pay for it. Conversely, if I invite someone to do something, I pay. The OP didn't address who invited whom though, so who knows what went down."

That's fine for one-off occasions, like inviting someone out to lunch or to the movies. But when you're someone's houseguest (even if they invited you!) it's outrageous to not bring your friend a present, take them out to dinner, etc. as a thank you. It's polite to make an offer to help defray costs of gas, tickets, stuff like that... even if you think they'll decline. Letting them plan and pay for everything for the entire stay is inexcusable.