It will eventually cost money, but then as with any commercial product you don't have to use it. There is currently a free Rust plugin for IntelliJ (to be deprecated, but will remain free and open source). There may also be a rust plugin for Eclipse (which is another alternative. I haven't looked into this). There is always vim if you want free!
As to being a cash cow, in my experience IntelliJ is the most used IDE (for Java certainly) in the commercial environment, probably as it is one of the best! And the reason it is one of the best may be due to the fact that JetBrains can afford to pay dedicated developers. (As a Software Developer myself, I can appreciate being paid for what I do!)
I will hopefully get RustRover included in my All Products Pack subscription, which I pay for. I'm happy to pay for this as I consider it an investment in my career (in the same way I consider the books I purchase an investment in my career). If you don't need to invest in your career, then by all means wait for the free alternatives, but don't begrudge those who produce (or purchase) the commercial products.