Good question, and one of the trickier aspects of the EWB Challenge,
The EWB Challenge design brief does not specify a budget or maximum cost that a project must fit within as every project may vary in complexity and scale depending on the project aims. In tackling budget concerns, we have outlined great tips on EWB Challenge FAQs. In this guide, we mentioned that in our design considerations, you might think about the ‘Capital Expenditure’ (initial cost to start) and Operational Expenditure (ongoing costs over time), which might include material and implementation costs, operation/program delivery costs, and maintenance costs. Ultimately it will be up to your team to decide what is a reasonable budget based on the value your design provides. You can justify a larger budget, for example, if you can demonstrate value for money such as longevity of your solution with minimal maintenance required.
I hope this helps, please reach out with any further questions!