Do I have full control over my monthly expenses?

Yes, you control spending via your plan choice. Free plan ($0, 5 daily credits up to 30/month) is most predictable. Pro ($25/month or $21 annually, 100/month credits) and Business ($50/month or $42 annually) have fixed costs. Overages aren't allowed—credits simply reset monthly. Use Plan mode (1 credit/message) for exploration to save Agent mode credits. Annual billing saves ~16%.