The free version is very capable and unless you make more than $100K dollars with it, you don't have to pay.
"Unity Free, which include the free platform add-on products, may not be licensed or used by a commercial entity with annual gross revenues (based on prior fiscal year) in excess of US$100,000, or by an educational, academic, non-profit or government entity with a total annual budget for the entire entity (based on prior fiscal year) in excess of US$100,000."
To expand on this, the free version is very capable and doesn't restrict the ability to publish your game. If you're an independent developer it's unlikely that you'll find yourself constrained.
Nitpick: an individual or entity with $100,000 in revenue per year cannot publish using the free version. Per their license[1], it does not matter where the revenue comes from. There is probably some sort of legal gymnastics you can perform to get around this, and one could argue that if you have $100k in revenue you shouldn't be worrying about a $1500 one-time purchase, but it is a limitation.
And $1500 is not expensive for a game engine, or really any type of professional content creation tool.