4 adults flying into Heathrow in June. Would like a car service to transfer us to hotel in Southampton. Looking for the least expensive way ..suggestions appreciated

Welcome to the Fodors Forums We added "Heathrow" to your thread's title and tagged it for the United Kingdom.

Welcome t Fodors. There is no 'least expensive' LHR to Southampton car service. Most charge about the same £160-£200-ish depending on the type of car and amount of luggage.

Are you catching a cruise in Southampton? If so the cruise line may run a coach or recommend a specific car service.

The cruise line will likely have some suggestions for you. I did find this website which mentions buses that go directly from the airport to Southampton and others that stop at Stonehenge which might be fun, if you have the time.
https://www.getyourguide.com/s?cq_sr...pton&et=486080

You did ask re a car/driver, but National Express runs a regular express coach from LHR. But it only runs every 2 hours so might or might fit your needs.

Since you mention a hotel I assume your cruise isn't sailing until at least the next day - right? Have you considered staying overnight in London instead? Trains from Waterloo Station go to Southampton about every 20 or 25 minutes throughout the day.