Upload & Sell: Off
150-200 euros a day for lodging is not bad for 2 people. Assume you would be renting a car? gas is pretty expensive two months ago it was at $2.19 per liter.
I would suggest taking a trip to jokulsarlon on the way to the glacier lagoon you will also pass Reynishverfi Beach, Mýrdalsjökull, Eyjafjallajökull, Skógafoss, Seljalandsfoss and Svatifoss... http://500px.com/photo/14282871 (which to me is the most worth it of these waterfalls).
For the rest of the days, I assume you would be aurora hunting at jokulsarlon, I suggest a trip to pingvellir national park, then on to snaefellsnes to see kirkjufell and the black church of budir. its a very nice area to explore and catch aurora as well.
personally I would do the highlands, and the western fjords as well but there looks to be no time left to squeeze those in.