Thanks to all of you! The four of us are really 'dreaming' of roadtripping for a month in the USA without watching the money and doing what we feel like doing while we still can. This is possibly our last trip together so we definitely want to make the most out of it.
We're going to check our options and routes carefully the coming weeks and try to increase our budget if possible, we all want to split all the costs (excluding some souvenirs for home of course). Since we're planning a long time ahead we think it's possible to increase our budget for this journey. We definitely want to try traveling for 28 days.
We indeed want to avoid tensions in the group, last year we were with a group of 8 in a small van, we had too many wishes and different interests to plan the optimal trip. We had spent €1200 on a 15-day journey, that's why we thought of the €3000 budget for this trip.
I (we) truly appreciate your responses and will use the given tips while planning ahead! If any more questions arise we know where to go ;-).