What are my options for cross browser testing in an environment where security is of high concern

I am looking for options to set up cross browser testing at our organization. Our clients use only IE 9 and up so my test environment will only require IE 9/10/11/Edge and should allow the tester to ma

Due to the nature of our work security is of high concern so we cannot invest in any tool unless we are absolutely sure that the probability of a compromise is minimal. I am currently looking into Browserstack and Saucelabs. I had also looked into modern.ie but it's licensing does not allow it to be used for 'commercial' purposes.

Would love to hear what has worked for others in similar situations.