I was lucky when my engine went that there was a near-new second hand one on eBay for 1k. I was told it was out of a 159 supplied for filming the last Bond movie so I wonder if there may be some others knocking about?
Apparantly, Alfa quote 19hours to swap an engine out in a 159/Brera but understand it is usually done quicker.
To give you a ball park idea, my total bill for the work, engine, gearbox (it was with the engine), radiator and a few other bits was 3k.
I had the work done by a garage in London as they already had the engine but after many recommendations, would have had it done by Autolusso if circumstances were different. Saying that, the guys that did mine did a cracking job (touch wood!).
Through enquiries on the net, I was also pestered many times by companies offering to re-manufacture my old engine and have everything up and running for about 2k.
I'm sure Ned will be able to advise you further and let me know if my old block can be of any help to you.
Once you get a plan of action, you can then start thinking about what modifications would be economically prudent to do at the same time