Your crib is not a hotel or a bed and breakfast. The fact that your friends want to come to the city and engage in overrated tourist activities is far from your problem. Plus, you don't want to hear their whining about your lack of internet and your bare fridge. When you get the "Can I crash at your place?" call, kindly refer them to one of those travel search engines where they can name their own price.
Don't worry about burning any bridges; you don't have money to travel anyway. You won't need to sleep on their couch any time soon.