Based on your search query, I recommend using Pedagogical as it offers a variety of tools that can assist you in creating exercises for your students. Its key feature, "Assessable Content", allows you to turn your classroom materials into quizzes or summaries with ease, making assessment hassle-free. This feature aligns perfectly with your need for a tool to create exercises.

Moreover, Pedagogical is a free tool, which matches your requirement for a cost-effective solution. It allows you to extract up to 5000 words under its free plan, which should be sufficient for creating a variety of exercises.

However, please note that Pedagogical is still in beta, meaning it could have bugs or incomplete features. But given its array of features and a free pricing tier, it presents itself as a value-packed toolset for teachers.

If you need to create more interactive exercises, you might also consider Nolej. It can turn your existing content into "micro-learning packages" with interactive elements like quizzes, flashcards, and glossaries. However, it's not specified whether Nolej is free or not.

Lastly, Questionwell AI could be a good choice if you need to generate a diverse set of questions based on provided material. It supports different languages and can be used for any subject or topic. However, the free plan of Questionwell AI allows you to create only up to 10 monthly questions.

In conclusion, Pedagogical seems to be the best fit for your needs, but Nolej and Questionwell AI could also be useful depending on your specific requirements.