Depending on what kind of shot gun you have, there may be some after-market barrels available. A friend of mine bought a Mossberg produced barrel for his 870 very reasonable and it works fine. Depending on the gun, a cantilevered barrel (integral scope mount) may be available and is a superior set up.
IMHO, if your going to be hunting in Illinois the rest of your life and can afford it, might as well buy the rifled barrel/gun. Smooth bore will work fine; rifled is superior (but also more expensive to shoot).