Orange Mobicartes are sold at eBay.fr for less than € 20. Last year I got mine for € 9 or so, but you need to check, which sellers ship overseas and what they charge for postage:
orange mobicarte, Téléphonie, Mobilité, Collections sur eBay - Achetez, vendez!
Regarding mail traffic, yes you'll be charged after exceeding 10MB of traffic over any mail protocol, which does not only include SMTP, but also POP3 and IMAP. So better use a webmailer if available!