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Try carpet scraps! Most carpet wholesellers and resellers will have small portions of carpet that they are unable to sell and get thrown in a scrap pile. Most are willing to sell it at a very discounted price. I'm sure you can find it online for cheap as well. The problem with curtains is that they are not thick enough to be effective at noise cancelling, unless you purchase a large quantity. Carpet scraps might be cheaper in the long run. Either way, an extra layer of carpet or a curtain will make a difference and is cheaper/faster than an additional layer of sheetrock/drywall.

Oh, I meant noise canceling curtains. That is why I came to 2500 for just the bedroom that is quite small. That is way too much off course. But I will look for carpet sellers, that isn't a bad idea.