Make sure you check out a pc tablet before buying.
Acer has the Iconia tablet running Windows 7. It is about $500 and around the same size as an ipad, though heavier.
Here's the thing about tablets. Tablets running windows will provide the most versatility for PALS and can be adapted for continued use once a PALS loses the use of their hands. They have usb ports for peripheral devices and most AAC programs are developed for Windows. However, be aware that, unlike the ipad and android tablets, Windows was not designed for a touch screen interface. So windows tablets are not great touchscreen devices, but can better adapt to changing needs.
If you are interested in portability, see if a netbook will suit your needs, as they are the best value. If portability is not an issue, stick with a regular laptop.