For that very reason I've been buying charts online from European suppliers for the last few years.
Google 'Boutique Aero' and 'Boutique du Pilote' for example for French charts. I have used both of them with no problems. The delivery times are slower than with some UK suppliers; about two weeks for the 2007 French IGN and SIA VFR charts which I have just received, but it does save a good deal of money.
The savings do vary of course - I need Norwegian VFR charts for June and they are at their most expensive at Transair and Flightstore; AFE are about a fiver less whereas the Norweigian Aero Club's online store is another few pounds less than that.
For a single foreign chart the postage could cancel out the savings, but if you're buying several it's an option worth looking at.