You could just do the obvious thing! Get a a less expensive new wacom tablet bamboo for like 50$ that can do anything you want and will let you experiment and not make you invest too much mone. Option a you will use it once and a while and it will be awesome option b you will use it non stop and get very good and realize after a while you need a sharper ride , so you will sale that bamboo and get a fancy shmancy intuitos
I know you stated you want Intuos 3 or later, but I have a large Intuos 2 Wacom Tablet (23.5x17.5). I just decided about 2 days ago that I want to sell it, because I'm wanting to get a newer and smaller wacom. The Intuos 2 comes with the tablet pen and pen stand. And it's in good condition. No problems with it as far as I know. I had a couple offers on it already, but no one seems to be serious about it. How much are you looking to spend?
eek!, that's alot for a used tablet, the full listed price on the wacom site is £329, amazon does an intuos 5 medium tablet for £274, brand new (don't worry i brought mine from there for that price) pc world - don't go there, if you are buy an intuos (new or used), you won't get a warranty from the store, they're also expensive as well i also found a intuos 4 wireless (the workspace is a similar size to a small, you might as well buy intuos 5 medium without touch for the same price) on the wacom store for about £230 and intuos 4 small for £115 (same price as a bamboo fun & touch small) [link]