Unlike models with lots of memory, the Pi3 1GB and Pi4 1GB are still cheap, but the Pi4 1GB is sold out everywhere. I think the Pi4 is sweet spot for small projects.
I have many varieties of Pi, but my favorite (overall) is the Pi400 (mine has 4gb, but that built-in keyboard!). The 3b+ is great for one-task projects that don't need [much/any] local input.