Quick check on prices gives about 240 euros for a small printer (6 by 4 inch prints only), 8 euros for 20 sheets of paper. That means about 4800 prints before you can match the price of a printing shop selling at 45 cents a print, and note that I'm not yet counting the price of the ink here!! (Couldn't find the price of that) Another assumption is that the printer will not break down during that time
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I'd say stick to a normal inkjet printer for the occasional print and use a professional service for the bigger jobs.