Salary and Rate fields are stored in the Contact Record on the General tab.
Salary and Rate data is available in Mercury Legacy Search. After you've created your initial search criteria or used a saved search, click the Filter icon on the left.
Adjust the Rate and Salary sliders to what your desired criteria is > click Confirm.
Results will then adjust based on the changes you just made, pulling back only Candidates who meet those Salary and Rate requirements.