I did a huge amount of research on what to do with prints, I very quickly worked out unless you were sure you would sell many of 1 print it was easier and cheaper to do it yourself, ok I'm the first to admit, they are not the same top quality as the fine art ones, but with matt archival paper and good quality inks that are lightfast, a bit of adjustment on printer settings for colour and brightness, you can get a decent A4 print to sell.
The biggest challenge I found with fine art printing companies is the set up cost of a print, you also need to colour match it, so a proof is required, most of the main online ones I looked at charged around £40 set up and about £12 proof. The 2nd challenge is having a high enough quality photo over 300DPI, this poses a few problems with your normal digital compact camera giving a decent image, so the alternative is posting your work to them for scanning.
If the costs don't make you run for the hills then I would say Abacus looked the best to me. Its the one I'd choose if 1 of my prints starts selling alot.
The other alternative would be to go to your local printing company, if they can scan your work and produce a digital print and colour match it, I do this for greetings cards and they don't charge me for a proof, but I do order over 500 cards at a time to keep costs down.
I do know other artists who have e mailed photos to local printing companies, and they have done a A3 print out for £2.50 each, no colour match or proof. The colours are not the same as the original, the quality of the image is not sharp, but they have sold them, it wouldn't be my choice, but as my artist friend said, its a print, it does not have to be perfect, its not the original, if someone likes it they will buy it.
Hope this helps....Lynn