I was looking for an online image of this wonderful portrait of Martin Clunes by Trevor Leighton (believe me the thumbnail doesn't do it justice). Google threw up a link to the National Portrait Gallery, and I was pleasantly surprised to see that they were selling prints at rather good prices. An A4 print for £5 or an A2 print for £12.50 seems a bargain to me. So its not going to be an investment, but its an affordable way of getting prints and helping to keep the National Portrait Gallery going.
While you are at it, why don't you go down there and have a look. Entry is free, but you do have to pay to see the Vanity Fair Portraits, which should prove to be a good show.