John,
I don't think anyone uses HP for "proper" printing much these days, most seem to opt for either the Canon Pixma Pro range or, as Andy says, one of the very good Epson A3 printers. This choice generally seems to be down to personal choice as both manufacturers have come up with excellent ranges of A3 printers and they are pretty evenly matched cost wise.
I can't pass comment on Epson as I have never had one, not even an office AIO but I can recommend the Canon Pixma Pro-100 which will come in within your price range.
Either way can I suggest you make sure that you have enough room to house the printer. I'm not sure about the Epson A3 versions but the Canon I have is huge and needs about 10" behind it as the A3 paper is rear fed. Also remember that they are bloody heavy!
Also, can I echo Andy's comments re the running costs. Whilst these printers have separate colours of ink (my Canon has 8 and the next version up has 10 if memory serves me well) it is generally the paper that is expensive. Unless you have experience of what papers work well etc may I suggest getting one of the many "trial" packs that can be bought easily enough. These contain different types of the makers main paper.
Another thing that I had forgotten about was the necessity to have good colour collaboration. At the very least you will need to have a calibrated monitor, then there is the question of printing profiles. All in all it is a very in depth aspect of digital photography, I have watched countless video's on You Tube, read a lot of books and still feel as though I am only beginning to scratch the surface of home printing.
I am not trying to put you or anyone else off but, as I have found out, it is not just a case of plug in and print, well not if you want decent results
Andy