A bit offtopic but tell me - Screen tablets like Cyntiq can work standalone with no pc ?
Only if you pick the Cintiq Companion. This is a "Tablet" in todays meaning of the word, which means a mobile device with an integrated screen, touch and in this case pen digitizer, and all the internals needed (CPU, GPU, Memory, SSD Storage) to run standalone.
There are two versions: The companion, which is a mobile Windows Workstation with the internals of a typical Windows laptop, and the companion hybrid, which is the Android version with the internals of a powerful android tablet, and the ability to be turned into a normal Cintiq "Graphic Tablet" when hooked up to your PC.
Both are virtually identical outside besides the ports to the Cintiq 13, which is the smallest of the "normal" Cintiqs of the current Cintiq Line.
"normal" Cintiqs are just screens with a digitizer layer over them. So they cannot work without being hooked up to a PC as they have no CPU, GPU or Memory in them.
The companions cost around 1200-1500$ for the Android version and around 2000-2300$ for the windows version, depending on internal SSD Size.
The normal Cintiqs cost around 900$ for the 13HD, around 1800$ for the 22HD and around 2300 for the 24HD version. There is a newer version of the 24HD incorporating Touch and a 10bit Panel, this is conisderably more expensive than the 24HD costing over 3000$ though.