SwissPostCard will send a personalised (photo upload possible) card world wide with priority mail for 2.90 Fr (15cm*10cm) or 3.90 (21cm*15cm).

There is also an assistant called MailingCreator which allows you to upload addresses in .txt, .xls, .csv and Outlook format and manually. The price for 200 cards would be 1.70 Fr./card with economy mail or 1.90 Fr./card priority, no matter if the cards are A5 or A6 formatted.

The entire service is available in English. I tested it in its early days and found the cards a bit thin. The image resolution was downscaled before printing, other than that it was okay. Maybe the quality has improved or you find it sufficient anyway - At 4 Fr. you can give it a shot I think.

If you do so, please tell me how you like it!