REGEX-Escape for: /checkout.html?affiliate=A01&evid=11853320&fun=page&pagename=event

Your Input:
Result, the escaped string:
\/checkout\.html\?affiliate\=A01&evid\=11853320&fun\=page&pagename\=event

What must the escaping look like for:
/checkout.html?affiliate=A01&evid=11853320&fun=page&pagename=event

The excaped text for use in a regex is:
\/checkout\.html\?affiliate\=A01&evid\=11853320&fun\=page&pagename\=event