If you don't already have all the information you are looking for, I have a little more. This is only looking at Bricklink and not Lego Pick a Brick.
Brickficiency is a program that most people aren't aware of. It is a tool that can import an xml wanted list from Bricklink and calculate the lowest number of stores your list is contained in as well as cost (before shipping of course). I ran this on a parted out list for the 10185 Green Grocer including Minifigs and excluding instructions. At first I ran the tool only looking for stores in the North America. It got through 3 store combinations with no luck and 4 store combos will take HOURS to calculate. I expanded the tool to look at stores in all countries, here is what it found in 10 or so minutes before stopping the calculation.
2 Store Combo - 1 Solution
Total - $1502.06 from 1 Portugal and 1 UK store
3 Store Combo - 3 Solutions
Match #1 - Total $884.47 from 1 NY, USA - 1 Portugal - 1 UK (Portugal and UK are the same as in the 2 store combo)
Match #2 - Total $1049.02
Match #3 - Total $1479.58
4 Store Combo - 2 Solutions
Match #1 - Total $847.03 from 1 NY, USA - 1 OR, USA - 1 Portugal - 1 UK (NY, Portugal and UK are the same as in the 3 store combo)
Match #2 - Total $881.01
There may be better combos if you let the tool run all day. And as many have already mentioned if you substitute out some of the more expensive parts (1x8 Sand Green) with smaller parts it could cut the cost greatly. That 1x8 in the Match #1 of 3 stores was running $3.55 each, x 50 = $177.50. The 1x2 Sand Green w/ Groove is also a larger cost at $184.24. There is nothing really to get around that part. Those two parts are making up for 42% of your cost.
Seeing as you can get a used set starting around $650, finding all the exact parts isn't worth it. (BL pricing)
Hope this info helps.