Would it not be cheaper to just have a boxful of stuff posted from back home?
No....because the Poczta will steal or lose it and you will be out even more money. In the odd chance it makes it through they will add taxes and "fees" to make it cost more than if you bought it at their locally inflated costs to begin with.
You can be rest assured that if there is the slightest chance you can somehow get a good deal for yourself someone here (govt/shops whoever) will find a way to make themselves a profit on it and screw you out of any discount you may have found.