String format currency

You need to provide an IFormatProvider:

@String.Format(new CultureInfo("en-US"), "{0:C}", @price)

As others have said, you can achieve this through an IFormatProvider. But bear in mind that currency formatting goes well beyond the currency symbol. For example a correctly-formatted price in the US may be "$ 12.50" but in France this would be written "12,50 $" (the decimal point is different as is the position of the currency symbol). You don't want to lose this culture-appropriate formatting just for the sake of changing the currency symbol. And the good news is that you don't have to, as this code demonstrates:

var cultureInfo = Thread.CurrentThread.CurrentCulture;   // You can also hardcode the culture, e.g. var cultureInfo = new CultureInfo("fr-FR"), but then you lose culture-specific formatting such as decimal point (. or ,) or the position of the currency symbol (before or after)
var numberFormatInfo = (NumberFormatInfo)cultureInfo.NumberFormat.Clone();
numberFormatInfo.CurrencySymbol = "€"; // Replace with "$" or "£" or whatever you need

var price = 12.3m;
var formattedPrice = price.ToString("C", numberFormatInfo); // Output: "€ 12.30" if the CurrentCulture is "en-US", "12,30 €" if the CurrentCulture is "fr-FR".

I strongly suspect the problem is simply that the current culture of the thread handling the request isn't set appropriately.

You can either set it for the whole request, or specify the culture while formatting. Either way, I would suggest not use string.Format with a composite format unless you really have more than one thing to format (or a wider message). Instead, I'd use:

@price.ToString("C", culture)

It just makes it somewhat simpler.

EDIT: Given your comment, it sounds like you may well want to use a UK culture regardless of the culture of the user. So again, either set the UK culture as the thread culture for the whole request, or possibly introduce your own helper class with a "constant":

public static class Cultures
{
    public static readonly CultureInfo UnitedKingdom = 
        CultureInfo.GetCultureInfo("en-GB");
}

Then:

@price.ToString("C", Cultures.UnitedKingdom)

In my experience, having a "named" set of cultures like this makes the code using it considerably simpler to read, and you don't need to get the string right in multiple places.