I've just picked up a used Pixma 4300 off ebay solely for printing on to discs. £30. The 4850 available for £67 off Amazon was my benchmark when judging what to get. Ultimately I didn't get the 4850 but chose a much cheaper and used earlier model because it will be used only for discs. All the 4000 series do discs.
When I first started looking, around a month ago, I read that third party cartridges weren't yet available for the 4850, if that's of any concern to you. The chips haven't been cracked yet.
I gave up looking at HP because there was absolutely no info on whether they would do discs, neither in the detailed specs on sales sites, HP's site, nor used ones on ebay. I won't touch Epson because with the limited use it would get the jets would inevitably block.