1. Ultra mobility: 10.4 or 12.1 inch models. Go for either the HP TC1100 or Acer TMC111 for 10.4, or Fujitsu T3010 for 12.1 (too bad the Toshiba M200 is over $2000). Unfortunately, drawing on 12 or even worse 10 inch screens are no fun at all, At least for me (got big hands.... for an Asian....).
2. Low mobility: 14.1 inch models will provide better much more freeing drawing area size. As big as it gets for TPCs right now. Acer C302 and Gateway M275 are your choices. As a bonus, these come with optical drives built in. The con is that they are heavy.
3. No mobility: Wacom Cintiq 15X has been lowered to $1500, and is a much better drawing device than any TPC since it's bigger, has more pressure sensitivity, has MUCH better screen quality than any TPC screens, and can be mated to any fast computer (one that you already have perhaps). And if you don't have your own computer right now, you can build an awesome 2D PC for $500 easily, so technically, $2000 will get you a non- mobile TPC this way. ;)
Some things to keep in mind: To use Painter 8 effectively, you should have at least 1GB of RAM (I have 2GB of RAM and even then Painter 8 complains about lack of RAM when building brushes over 100 pixels). Getting 1GB of RAM with TPCs would probably take you over $2000, since 512MB DDR SODIMMs are expensive, and you only can have 2 slot in TPCs and laptops. Less of a problem to get 1GB of RAM on desktops, especially if you have a mobo with 4 DIMM slots (like I do).
My personal recommendation as a Painter user on a Cintiq and a TPC: If you don't need to be mobile (notice I said "need", not "like to". We all would like to be mobile all the time. And we all would like to be millionaires too ;)), then you should definitely get a Cintiq 15X over a TPC. Much better Painter experience on a Cintiq. Trust me on this one.