A good instrument takes time, research, testing, and money to create. That's why test creators, such ETS, don't give their instruments away for free, but sell them as a product they funded to create. It can get expensive because you don't simply purchase the instrument, but the key, and an evaluation tool explaining what the results mean. Obtaining a well respected instrument may require a grant. And even purchasing an instrument often means filling out a form explaining who you are and how you are going to use the instrument. Publishers don't want to degrade the integrety of their instruments by having it misused by unqualified people.
If you don't have the means to use an expensive instrument, you will need to find one another way. Use the drop-down menu for this section to find a wealth of resources to help with finding instruments.