The information you're after is probably in the London Airports forum, as opposed to Travel.

If you decide to do this by cab, you'll have to be well aware of the luggage limitations. You would also need to book in advance - a black cab could refuse to take you, but if they did, I'd suspect it would be well over £100, probably £150. It wouldn't be comfortable, either.

A lot of car firms use people carriers, typically the Renault Espace. This will seat up to 6 but has limited luggage space.

I would suggest you take the coach (www.nationalexpress.com) - runs every hour, and you won't have any problems with luggage.

The other alternative is HEX to Paddington, tube to Liverpool Street, then train to Stansted (if it's running, which it often isn't at weekends) - between 1.5 and 2 hrs, about £25 each one way.