This is not perfect. Might find a better regular expression, but it should work for you:
string re2 = "(?<=^|,)(\"(?:[^\"]|\"\")*\"|[^,]*)";
var regex = new System.Text.RegularExpressions.Regex(re2);
var str = "Alice,5000,14.15,\"70,750.00 \", \"I have a \"\" in this\"";
var results = regex.Matches(str);
var arrayResults = results.Cast<Match>().Select(m => m.Groups[0].Value).ToArray();
foreach (var match in results)
{
if (match.ToString().IndexOf(",") > -1)
MessageBox.Show(string.Format("Found string '{0}' with comma.", match.ToString()));
}