This, or rather what follows, is my first post of any kind on this or any other forum. So, first time caller and all that?

I had an accident last year in which the down tube of my Bianchi Via Nirone CTC was dented. I saught some advice at the time and as it was on the underside I decided it was safe to use - the stress on the tube going in the opposite direction.
So, maybe 14 or 15 months later I've found a small crack along the line of the dent and I'm now pretty sure the sensible thing is to replace the frame.

The bike is under two years old, but aside from the original Ultegra Groupset, I've upgraded everything else on the bike and want to transfer all components to a new frame? and this is where my conundrums begin;

I don't want to fork out the ?300-400 for a more or less direct replacement - not least becaue I never really thought it was the greatest frame anyway. I've seen Tifosi and Genesis (amongst others, inc second hand) at much more reasonable prices, ?150 - 220, but don't know if the Bianchi forks and seat-post will transfer, or whether they need replacing.

So what snags (they are inevitable) should I be looking out for, what's compatible and what's not? I've seen Sheldon Browns list of seatpost diameters but everything seems older - is it really that complicated for new bikes?

Also, any thoughts on the frame damage? I would have described it as structurally sound before the crack emerged, but clearly this only goes so far. Is there a solution?