Summarise data based on date

Hi There,

I have a set of data in excel that looks like this:

Project Name alpha date alpha price beta date beta price final date final price
Project a 1/01/2013 $123.00 2/02/2013 $324.00 5/02/2013 $222.00
Project b 2/01/2013 $432.00 9/03/2013 $111.00 30/03/2013 $321.00
project c 2/02/2013 $4,431.00 8/03/2013 $231.00 7/04/2013 $343.00
project d 3/04/2013 $1,232.00 30/01/1906 $3,122.00 6/07/2013 $666.00

I need to generate a sum for each month/year across all projects and phases of the project. IE:
Jan 2013 $555
Feb 2013 $4,977

What's the best way of going about this?

Sample Data.xlsx
here is an example of what I'm trying to achieve (calculations done manually)

Originally Posted by AlKey

For Alpha:

=SUMPRODUCT((TEXT($B$5:$B$10,"MMMM")=TEXT(K$4,"MMMM"))*$C$5:$C$10)

This worked perfectly! Thanks!

Now to add another layer of complexity...

v2 Sample Data.xlsx

In this file I have 'forecast alpha price' and 'alpha price'

I need to do a formula so as IF 'alpha price' is blank, use 'forecast alpha price' else, use the value in 'alpha price'. (and likewise for beta and final)... thoughts?