I'm not sure about what "willing to" means, but google translator says "estou disposto a + infinitive", which I believe is right. At least the portuguese sentence makes a lot of sense.
It meas that I'm decided / prepared / intending to do something, even if I have to spend a lot (of money, energy, time...)
Not exactly, accept to means you will, which is definite, willing means accept to if asked. Consenting in other words, and depending on the context more or less enthusiastically. It can contain an element of reluctance, eg I'm willing to go to the doctor (but without much enthusiasm, as opposed to happy to go), but it depends on how it's qualified. "Ready and willing" or "ready, willing and able" are well-known sayings, they mean enthusiastic to do something.
It can sometimes have sexual innuendo. I don't know if you're a heavy metal fan Dan, you look like you might be.
Thanks, Paulenrique. Mine was a shot in the dark and it was really off the mark. :) You're right, but after some research I have found there is actually a better way to explain this expression to a native speaker of English. It is funny how everybody above missed it because it is super simple and straightforward. "A fim de" means "In order to". It is an expression of purpose. Another word in English to express purpose is "for". A litteral but actually very idiomatic translation for "Estar a fim de" is "to be for" something. This translation will work every time "A fim de" is used to express an adherence to an idea or a course of action, although it will not really work when "a fim de" is used to indicate an interest in something or someone. Still, in the current exercize, it is the closest translation and perhaps the best answer. "I'm for seeing the city."
I'm not inventing this. Please see the links below.
My main goal was to answer the very first post of this thread. To a non-native speaker of Portuguese, this expression seems to come out of nowhere, to have no logic at all. What I meant to demonstrate is the logic behind using "a fim de" as an expression of feeling or desire. It is a subtle shift of meaning, and I was trying to show that a similar shift was also present in colloquial English.
Of course, "I feel like..." is the most natural way of translating "estou a fim de". And it also works for "tenho vontade de" and other similar expressions. I was trying to find an expression in English that would be just as weird, semantically, as "estou a fim de..." (which I know doesn't seem weird to a native speaker of Portuguese). Granted, the use of "I am for" in this situation is not common, but it makes sense. And more importantly, it will help native speakers of English make sense of "estou a fim de".