22 minutes quicker than the Flibco shuttle (sold from £6.99), for about the same starting price. And no booking needed.
National Express coach
National Express · National ExpressPickup, hours & luggage
Boards at. Coach station, a two-minute walk from the terminal
Three sources give three starting prices: "from GBP 5" (the airport), "from just GBP 7" (National Express route pages, used here), and "from GBP 10.50 one-way including a GBP 1.50 booking fee" (National Express's Stansted hub). A 33 per cent group discount applies to four or more, on single journeys only, with code GRPAPT33 — a percentage, so it cannot be priced into a total here.
Luggage. One suitcase up to 20 kg and one hand bag up to 10 kg per person.