After some research we came to the conclusion, concrete blocks and mdf will do the trick. 2 mdf boards, pretty much any size will do but we settled for 400x2480x18mm. To accompany that size mdf 6 concrete blocks were bought at the same company, size 390x190x138mm (weighing 22kg each).
The next step we thought about even longer (a year after the initial bench was done). We didn't want the tv standing ontop of the bench, we both hate the tv-stands and thought of the idea to have a (what we call) tv neck. Two days later and the blueprint was ready and sent to our local sheet metal shop for laser cutting and bending. We got a good price for the 2mm sheet metal (I guess they had some jobs already for that sheet metal) and two weeks later we had the tv neck (in pieces) in our hands. A friend of ours work as a welder and after buying him a lunch and coffee we got the neck welded. Some powder coating later and the results is as shown in the pictures. Please feel free to use the blue prints of the tv neck. It is constructed in a way that it should be fairly easy to weld. The neck itself may store much slack cables and should work with any flat screen tv. Thank you for your time, I hope you'll find some bits of good information.
PS. all in all the bench set us back around $190 (1250 SEK)... and for that we got ourselves a 100% custom made bench.
EDIT1: added simple pdf that show the foot of the tv neck. I think I'd might make a better blue print later...