Emily is organizing a charity event where she needs to prepare gift bags. Each gift bag contains 4 items, and she can assemble 5 gift bags in 30 minutes. The cost of each item is $2.50. If Emily has 3 hours to work on assembling the gift bags, how much will she spend on the items for all the gift bags she assembles? Let's think step by step and output the final answer within \boxed{}.
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