Right now, my main portable system is just a Westone ES2 out of, right now, an iAudio 7. I don't really need much more than that since the ES2 is very easy to drive while still sounding like a proper high-end headphone.
Total cost: $800 give or take. I could throw an amp in there for anothe $400 but the ES2 is so easy to drive that there's no point.
My more bulky portable system is... well, I'll keep the details to myself, but let's just say that it consists of a unique, DIY modified Stax SR-001 system, sourced from a MicroDAC out of a Sony D-NE920 CDP. It sounds absolutely brilliant, but I'll say no more.
Total cost: irrelevant, since this is a unique mod and there will never be another one like it.