Here is a nice concise post on how to display a value (of double type) as a currency (string) using the format of the culture of the local machine
http://geekswithblogs.net/dtotzke/articles/24573.aspx
An article from MSDN on the same:
msdn2.microsoft.com/en-us/library/shxtf045.aspx
And here is how to convert a string represenation to a double:
System.Globalization.
CultureInfo ci = new System.Globalization.CultureInfo("es-ES");
string currency = "1.200,89";
double d = double.Parse(currency, ci);