Your price for buildable land in Europe is way off. The average price for land that is ready to build on in germany is around 129€ ( http://www.destatis.de/jetspeed/portal/cms/Sites/destatis/In... ), resulting in about $700,000/acre. Towns are quite a bit more expensive.
Think you'd have to look at the term "buildable"... the US doesn't try very hard to prevent urban sprawl with it zoning rules. The EU, in comparison, may restrict zoning and in particular restrict the conversion of agricultural land into housing tracts.
