Is there a free way I can "paint" with prefabs?

I’m making a dungeon/puzzle game, and it’s getting really annoying placing my wall prefab by dragging and dropping. I see tools for using them at ~$15, something not in my budget of broke. Does anyone have a suggestion of something to do this, like a map editor?

The only free way is to write your own editor script.

I had a similar problem but i was too lazy to write my own prefab brush so i bought an asset for 6 bucks.