Sure, to a large extent existing in the US costs money, and you'd need to spend some on transportation or pay a premium to live in a walkable area. But beyond that there are still affordable activities you could do. Some things I've done in the US which only cost me the price of transportation:

• Aforementioned frisbee in the park
• Hiking with friends (met one of them at work, joined his group, brought a lunch box)
• Various activities at a local community center or library (not all places have one, some places churches are the closest you can get)
• Attended a weekly meetup about a topic I was interested in
• Chatted with someone while waiting in a line

Sure, a lot of the more affordable activities you'll probably only be able to do once a week. You can do multiple activities. Sometimes you meet friends who invite you to other activities. Help, I have too many activities!