User blog comment:The Milkman/The Definitive Mass Effect Experience?/@comment-5272419-20121103041351/@comment-5267262-20121103105546

In that case steam is your friend if you want to get the last part quite cheeply (assuming the missing section is 1 or 2). If you try getting ME1 on amazon it can end up many times more expensive than steam for a new copy and roughly the steam sale price for the cheapest used copy.