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...to the OP: I have been poor and in college in the past, and dependent on a bike for getting around. If it does turn out that one of your rear cogs is a little worn and the new chain is skipping on it, it is often possible to find another cog that you did not use much because it was not your preferred gear to ride around in, and use that safely until you have enough cash to buy the cog cassette or freewheel you require and the tools to change them out.

Generally speaking, it's great to have every cog working reliably, but sometimes you gotta do what you gotta do.