cheapest parking near baltimore aquarium?

we live in pennsylvania and have signed up for membership at the baltimore aqarium this year. we have 2 small children (1 yr and 2 yrs) so we travel with strollers and bags so the light rail is not something we want to do right now. we typically park at the lot adjacent to the aqarium or gay st garage but we are ending up paying typically $15 for a couple hours in the aqarium, even with the coupon from the aquarium. does anyone know of any other discounts or places to park within reasonable walking distance pushing strollers to the aquarium?