I'm sensitive to the cost of shipping to, since I ship about 1000 packages a year to my customers. as well as get packages as a consumer.
I have to say that it's hard to get shipping below about $7 per package when all of the handling and material costs are factored in as well as the base cost of the shipping itself.
And shipping, including USPS, has been going up sharply over the last few years, so look for minimum shipping costs to rise too. It's either charge a fair price for shipping or hide that cost in the merchandise prices.
One way to minimize shipping costs is to place larger orders so shipping is a lower % of the total cost. When shipping is 10% of a $200 order, that hurts a lot less than when it's 30% of a $20 order
Even driving to pick up an order has its own cost for gas and the value of my time. It's seldom cost effective to drive very far compared to having the order shipped.