Hope we can help you!
As far as your chipin for lodging goes, maybe we can bring it under $350. Have you checked these out?
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Days Inn Silver Spring: $76/night; adjacent to the Red Line, which is also the line to get to CPACi
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Motel 6 Washington DC: $54/night; Red Line adjacent
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Travelodge Alexandria: $59/night; Blue Line adjacent, requires one transfer to get to CPAC
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Silver Spring Travelodge: $50/night; Red Line adjacent
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Also search at Airbnb, which indexes a number inexpensive (but often nice) alternative housing options.