According to the last Rust Foundation newsletter Marco Ieni (https://ieni.dev) has managed to bring down the Rust ecosystem's CI costs from $1M to practically nothing and, inexplicably, this is not being shouted about from the rooftops but is disseminated solely via being buried in a newsletter. 
> In Q1 [...] the monetary cost of running CI has been reduced from $1M to $300K.
>
> In Q2, Marco found even more savings, [which meant that the spend on] CI has been greatly reduced–possibly to zero!