I haven't. I certainly haven't looked at costs. You're right that the European community has adopted a slogan; I think it's “mother tongue plus two”. It's the idea that Europeans should learn not just a second but a third language.
The one thing I would observe is that learning a second official language is not a barrier to learning a third language; it's a bridge. Where I became most aware.... I guess there are two anecdotal experiences I've had in this regard. One was when, as a journalist, I went on one of the Team Canada trips to China. The federal government pulled together all the Chinese speakers in the region from various embassies. They also hired Canadians in China to work as guides and translators for what seemed like the hundreds of Canadians who were on that trip. What struck me about these very impressive young Canadians, some of whom had been studying in China or working in other parts of Asia--and I couldn't evaluate the quality of their Chinese--was that they were able to explain to the bus driver where we wanted to go and what time we needed to be picked up and so on. They were able to carry on quite vigorous conversations with people and explain things to us. Also, they were all bilingual in both Canadian official languages. Clearly, learning French for the English Canadians and English for the French Canadians was not a barrier to their learning Chinese; it was part of what led them to learning other languages.