For a registry office/town hall wedding, the cheapest possible total cost is in Denmark, and is € 512 (handheld service of € 295 plus the Government application fee of € 212).
This will include everything, there are no hidden extras, everything is included such as taxes, 2 copies of the International marriage certificate (In Danish, German, English, French & Spanish).
The only other costs you need to factor are your personal costs of Hotel, Travel, wedding Flowers, wedding cake wedding Photographer - if you want them. So the cost can be as little as € 512 or as much as you want it to be!