For those interested in something more lightweight than jQuery that supports the majority of commonly used functionality, give Zepto a try.
It has a compatible syntax at a third of the weight. It's very well suited to mobile.
With regards to the original post; it's fantastic to be doing things efficiently, but in the vast majority of circumstances I would presume that forcing the user's browser to download some additional kb of libraries is preferable to forcing the user to Google a currency conversion.