Power Store does not support a sliding scale like this for the item pricing, this is not supported in power store.
it would take a good amount of hand coding to implement this in power store.
it can be done using eCart though.
there are a couple of different strategies that could be used. If all items had the same quantity break points, you would just need to add columns for the prices to the cart object.
if the break points would be different for each product, you would need to add a column fro each hi-low break point / price combination to the cart object.
you could then create a calculation to determine the price based on the quantity.
the shipping rule can be created fairly easily on the shipping tab of the power store settings.
set the Base rate to 7.95 and the per item rate to 1.50.