ProProfs has some reasonable plans if you are a K-12 educator. You can have the Free plan which is free forever but you don't get some important features like the ability to track who took the quiz or any of the analytics. However, if you wanted those features, you could get the Test plan which is $3.97 a month. But if you wanted more features like groups and question banks, the Test & Tech plan ($5.97 a month) might be a better option for you. Those prices are really very reasonable and if you have a classroom website and want to use quizzes, I think ProProfs would be a great resource.
With ProProfs, if you just wanted your students to take a formative quiz that means nothing for their grade, you could use the Free account to have students test their own knowledge before and after a unit just for the sake of becoming aware of what they should know and what they do know (i.e., metacognition). Honestly, that's how I'm thinking of using ProProfs. If the quiz will be for a grade, then I will go back to our CMS (course management system). You might even think about creating an account that students could use to create a quiz for their peers. That could be a fun way for them to prepare for a test or even reteach a topic to their classmates. Try it out and let me know what you think.