What you are asking might well be the most difficult exercice imaginable: compare prices between countries, even continents.
If you want to compare prices between the UK and the US you certainly remember the very long thread about pricing transparency in the US in which you participated yourself here: http://www.pianoworld.com/ubb/ubb/ultimatebb.php?/topic/1/21049/5.html#000121
I added some comments in that thread too http://www.pianoworld.com/ubb/ubb/ultimatebb.php?/topic/1/21049/4.html#000081
and because after having read many pages of it and can only be concluded there is no transparency in the US at all, I will not try making price comparisons between the US and countries in Europe.
As you also know for the US some put forward the Larry Fine price list as a reference, but others will then question it's final relevance. Others refer to the Blue Book of Pianos as a pricing reference for the US (http://www.bluebookofpianos.com/wwwcatalog.htm), but then you read these prices are highly 'inflated'.
For Europe my impression is that for the traditional brands (i.e. excluding the skimmy private labels) prices are quite consistant throughout Europe.
* the recommended selling prices (MRSP) do not vary much from country to country; because they have to include VAT, they may vary slightly if you have e.g a country where the VAT rate is 21% (Belgium) or 19% (Germany, the Netherlands)
* the discounts on those MRSP also fit within a narrow range for these brands and accross Europe (10 - 15%)- stock clearance sales excluded; even the big internet sellers in Germany mostly stick to this (www.musicstore.de and www.thomann.de)
* France seems to be a bit on the highish side for Kawai (some 5% above e.g. Belgium, Germany)
* It appears to me that Yamaha might well be 'the biggest discounter' in Europe, e.g. in the UK aswell as in Germany.
* For Yamaha sales online one should always be aware there might be quite some parallel imports from other countries in Europe (e.g. one dealer buying overstocks from another).
* If a model from a known brand appears much favourably priced with one dealer care should be taken this is not an 'older' model (e.g. a Yamaha C from before the C-series model upgrade during the summer 2007) or a model that is being phased out (e.g. Petrof P III)
* Sometimes there are surprises indeed and one thinks there is a good deal to be made. E.g. Brodmann BG 187 for € 11,750.00 in Ireland http://www.precisionpianos.com/showroom....%21&posted=true
where the going price on the continent is between € 15,900.00 and 16,000.00. One should of course first check whether or not Precision Pianos' website is still up to date.
* When differences of 4 - 5% occur this is often related to the fact that some dealers do not automatically increase the price of a stock piano whenever there is the annual price increase, while others do as to anticipate stock. replacement.
* Do not forget to check transport charges when buying in a foreign country.
To summarize as I personally always look for value (that is including the dealer competences and service) and not for price, based on the above I was never tempted buying from another country that is hundreds of kms away.