The 3 tours we sell that stop at Sólheimasandur DC-3 leave from Reykjavík and Vík í Mýrdal. Most of them start in Reykjavík, so for anyone based in the capital there is nothing to arrange beforehand.
All 3 of them collect you from your accommodation or a designated stop, so the tour is the transport — there is nothing else to arrange and no timetable to read.
A seat on a day tour here starts at €121 and typically runs €152, per person, private charters excluded because those are priced per vehicle and would flatter the figure. There is no scheduled bus we can sell you to Sólheimasandur DC-3, so a guided day is the practical way in without a car.
The days themselves run from about 10 h to 13 h door to door, so check the length as carefully as the price — the cheapest seat is often the longest coach day. 3 different operators run here, which matters more without a car than with one: if the weather cancels your day, there is usually another departure rather than a lost trip.
Whatever gets you to the car park, the last stretch is on foot: about 4 km each way across open black sand with no shelter and nothing to navigate by. The shuttle bus from the road covers that walk, and in winter weather it is worth the fare.
Both work here. A car buys you the stops you want at the times you want them; a tour buys you not having to think about the road.
Cheapest way in without a car: a guided day tour from Reykjavík, from €121 per person.