I feel like I have bad friends?

Im in 8th grade, highschool next year. I feel like all my 'friends' use me for my money and to sleep over!! Literally, we all went out to the movies one day, and they 'forgot' there wallets' so I had to pay $60 bucks for there tickets and snacks. I just feel really used, and like it's not an actual friendship... Oh ya and they never let me come to there house often and we always have plans then my one friend just backs down the last minute ALWAYS! I have 3 days left of school, and my friends are all going to a different highschool next year. So, I was thinking of just spending the summer at my cottage so I won't have to hang out with them? I have friends at my cottage to hang out with. And they always make fun of me in front of my face and behind my back, idk if there trying to be funny but it hurts my feelings, should I still be friends with them or drop them?