Fares are usually pretty cheap on Metro -- call (713)635-4000 and they can help you figure out your fares and stops from Hobby. Don't fly into IAH if you can get a cheaper deal from Southwest into Hobby. IAH is too far from Webster and Johnson Space Center if you don't have a car or don't want to pay for a cab. There are a couple of bus stops in the area of your hotel. How are you planning to get into JSC? Or are you just going to the visitor center?