If another developer reviewed your code, how much time it would it take them, and how much is that time worth?

If you divide the 50 bucks by that number, you get a cost ratio. If it's lower than the ratio of (benefit expected by automatic code review) / (benefit expected by manual code review), it's worth using.

I guess we can speculate all we want; in the end, only experience will show if the service is worth it or not.