regex for <span> Tag

You might try

Regex regex = new Regex(@"<span class=""Price"" id=""\d+"">(.*)</span>");

in addition to what _Asif_ says, change you code as well:

Regex regex = new Regex("<span class="\Price\" id="553">(.*)</span>");

Has backslashes in the wrong place, and won't compile:

Regex regex = new Regex("<span class=\"Price\" id=\"\d{3}\">(.*)</span>");

"f our id is alpha-numeric product-id-543"
If you are going to use regexes, then you need to be able to make at least basic changes to them!

Regex regex = new Regex("<span class=\"Price\" id=\"\.+?\">(.*)</span>");

Should do it.

Get a copy of Expresso[^] - it's free, and it examines and generates Regular expressions.