How do I go to a store that's 20 minutes away without my parents knowing?

well next Monday I've got school off, and I want to go to this new store that opened up about 20 minutes (driving distance) away. the problem is, my mom doesn't let me go anywhere without her... she doesn't even let me go to the mall with my friends without "a parent or guardian present." I'm 15 by the way! my mom is working Monday and since I don't have a car, I figured I could catch the bus and ride it to the corner of the street where the store is. how could I pull this off? (ive never ridden public transit alone before, by the way... tips would be good) I've got plenty of money; I've got $200, and I'll probably only spend around $50 at the store. oh and asking one of my relatives or friends parents to take me is out of the question... first of all, they're all working. second, my mom doesn't like the company because they support gay rights... (which I do!) but that's beside the point. note: I've been somewhere alone before... many times. just never this far away or by public transit.