I have been twice with Daniel Bergman in July/August and like other posters cannot recommend him highly enough. I also have been on an unhosted trip with another photographer for 14 days last August and completely agree that many of the best places in the interior are only accessible by means of a solid substantial 4WD. There are many difficult and rough tracks and glacial river crossings some of which are very tricky.
For a short trip into the interior by SUV rather than a big 4WD you could go to Landmannalaugar park up and spend a nice day walking and taking photographs nearby. The camp site/ car park has a cafe/shop, showers and toilets. There are a couple of places to stay at Hrauneyjar which is on the way and is a good base for the area. One is a sort of hostel/petrol station and their better sister hotel a mile or so down the road. The route (f208) from the hotel to the camp site at Landmannalaugar is passible by a small SUV without too much trouble but do not be tempted to carry on the 208 route south on the way back. This is a seriously difficult road to drive even with a big truck. There is another route from the west which is called the F225 but this is a again a more difficult route for smaller vehicles.
On the route from the hotel to the camp site there are several places to stop which provide photo opportunities - lakes, vistas, calderas, lava fields and so on.
visit my website www.davidwatson.org.uk
for a few of my photos of the areas.
BTW I took my Hasselblad outfit and a sturdy tripod last time - it all worked very well. Have a great time.