A sound booth is the most common solution, in a wide range of quality and price, but definitely cheaper than rebuilding your home. The smaller cabins double as saunas - simultaneously. (Don't forget to protect your body protuberances against the bellows.)

Another idea is using an electronic accordion for practising, with headphones. The cheaper ones do not give you realistic bellows action, so that from time to time you must use the instrument on which you want to perform.