Buy the wedge shaped concrete blocks for retaining walls and stack them. They’re 79¢ each on sale.
Here's a link that may help:
Or you can find some rocks (big enough but you should be able to lift them easily) and make a circle. Very rustic looking and really inexpensive.
Here are a few ideas: https://www.hometalk.com/search/posts?filter=diy%20fire%20pit
Check first with your town/municipality office to check what the bylaws may be regarding having open fire pits in a residential area. Depending on where you live they may be prohibited due to fire concerns.
Mistee: maybe this will help