If you want empty space for the occasional outdoor party, I agree you don’t have many other options. On the other hand, if you want something nice to look at but still fairly low maintenance and cheap, I’d go for a meadow from seeds. Using seeds keeps the costs down a lot and you can put together your own mix by ordering online. After sowing you’re gonna have to do some weeding at the start of the season, but then the canopy will close up. At the end of the season (or depending on your species selection) you get to mow it down with a scythe! It’s more work than a lawn, will not always look pristine and may not be as useful, but it’s probably better for your local ecosystem. James Hitchmough, they guy who designed the flower meadows for the London Olympics, has written a pretty good book on the topic.