Hi:

I will address your second questin: How does a BA define software project cost?

1.)  Rigorously define the scope (i.e., extent) of the system.  With sofware, this is especially important as you can neither see, feel or touch software and therefore determining scope takes real work

2.)  Properly partition the system down into equal-size "chunks" small enough that you can estimate the amount of work required to develop one of the  chunks.

3.)  Multiply the cost for amount of work for one chunk by the total number of chunks.

4.)  Adjust for inefficiencies (idle time and such)

5.)  Get accounting to cost it all out

This approach is applicable for both Agile and non-agile projects.

Tony Markos