Actually I think the Birkin is more square than a HAC, but either way--it's just different!
I don't know the exact price difference between chevre and togo but if I recall correctly it's a few hundred dollars, US. There's also a thread or two around here on Birkin pricing, which is really useful. If you use the Search button (along the top up there ^^^) and search on "Birkin Price" or something, you should find several resources.
If there was a positive karma button option, I would give you loads!! You are SO helpfull!! (there is a positive karma button on another site I visit)