Kate Pugsley, who takes around four weeks to complete a commission (though long-haired pets take longer!). See Kate's Etsy shop for more information: a to-order pet portrait costs around £180, plus just over a tenner for postage from the US and comes painted and varnished onto 1/2-inch thick maple, 6x8 inches big. You need to send her a selection of good quality photos to work from.
She also paints and illustrates other things, check out her profile to see the relevant links. I particularly like her people portraits, some of which are rather surreal (though not these ones below; I just like their faces).