TOTAL: 4490. lets call it 5k. 4k if the engine is only 2k, 3500 if you can wire.
First I will fully support what Karl said about engine swap projects; they are always much more difficult and expensive than anticipated. And many never get completed (although that is also true for many car projects of all types).
With that being said, and looking at Odie's excellent post with his costs. I would think if you started with a complete Honda ('B' engine) car, and used the stock electronics, wiring, shifter, etc, etc, from it (assuming you chose the right year/model to get the preferred components). Then the additional build costs would mainly be the axle-shaft modification ($600-800), and misc metal/small parts ($300-500)....say under $1500. Add about $2000 (or less) for the complete car and the total could be around $3500. Naturally you can go anywhere from there with performance mods, upgrades, rebuilds, etc. But you could also resell what's left of the Honda car (-$500) and sell the Fiat engine/trans (-$200), and the total could even be under $3000.
Compare that against the cost of rebuilding the Fiat engine and trans. Or the cost of the conversion
kit for a "K" swap (not counting the actual K and related extras). Or the cost of building a performance SOHC engine. Even a stock B will be equal or better in performance than any SOHC build, and the Honda engine and trans will be much more reliable and robust. Naturally all of this is assuming you have the ability and equipment to do an engine swap of any kind.
But please don't get me wrong. I am NOT advocating that anyone run out and start building a engine swap. There are many potential reasons not to do such a large project. I'm merely stating my surprise at how affordable this COULD be done and considering how it compares to the options. For example, I will likely have that much invested into my turbo SOHC build by the time I'm done with it. And it won't be anywhere near the potential of a B swap, on so many levels. So maybe part of my reaction here is a bit of remorse for not considering this option further before starting on the turbo?