Practical attack on md5 hashing algorithm?
Passwords, $p$, when only secured with a hash function $H$ on the database as $H(p)$ for login systems, is vulnerable to finding pre-image or secondary pre-image attacks. 

Secondary pre-image : given $ H(p)$ find $p' \neq p$ s.t  $H(p)=H(p')$.

The famous rainbow tables are generated to more effectively find the pre-image or secondary pre-images. To countermeasure the rainbow tables, salt is one of the solutions.

As I can see from your problem there is a salt and these prevent the rainbow attacks. 


As a result, you cannot benefit from the salts.


The only choice is the brute force.

And as you noted;


AWS p3.x16 has the power of 450GH/s.