The 5th Ave. space that used to be a 99-cent store between Bergen and Dean is going to be offering pricier stuff pretty soon. Fitness Collective, the personal training business with another outpost on 7th Avenue in the Slope and one on Court Street in Cobble Hill, has leased the ground-floor and should be open sometime in August. The immediate area already has a few fitness places close by: There’s that boot camp place around the corner on Flatbush, a Pilates studio and yoga center a couple blocks further south, plus that gym on the corner of Union. Room for another in the mix?