Just look at any laptop with FullHD IPS screen, preferable 4 core processor (but can be 2 core, if you want really cheap), preferable some NVidia card, 8Gb or more RAM and HDD.

If you take time and will track ebay deals or refurbished items - it can be really cheap.

Thanks for the hints! MSI I think still too expensive for my purpose. Will have a look at some other options. Namely, this one looks good to me http://www.amazon.it/dp/B00SVI6O2G/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=6P5938PFILTO&coliid=I34YBB3BBDO1RK

If you have time....Try batch encoding your master files to something like 320x288 or 720x504...should be pretty quick on a modern computer. create your HD Premiere project, drag in the 'Off-Line' / 'Proxy' files/ low res files...right click on low res clips in timeline and choose 'Scale to fit frame' or something like that and edit away with no need to render complex transitions. once edit is locked, re-link media with you FULL res clips....grade...done! I used to have a very old dell laptop with a 1.6 celeron CPU and that was my only way i could edit on the go. I currently use a Sony vaio Fit i5, 8GB ram, Nvidia card, and my editing is done via a USB3 drive, im so impressed how good the USB3 ports are. My GH4 HD footage has a smooth playback in Premiere pro 5.5 via USB3, but sometimes wish i went for the i7 Sony laptop.

Thanks for the feedback!