Samantha works as a freelance graphic designer and charges $25 per hour for her work. She has a potential project that will take her 15 hours to complete, but she is also considering attending a 2-day design workshop that costs $300. If she attends the workshop, she will not be able to work on the project during that time. What is the opportunity cost of attending the workshop? Let's think step by step and output the final answer within \boxed{}.
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