how do you put it in your family inventory before exiting the buy mode? I don't recall/ remember how to do that.
Just to let you know I have the Xbox Version so buttons may be different. What I did was buy the collection helper and place it somewhere on the lot. Then I pressed 'Y' and the menu at the top right dropped down giving me options to Move, Sledgehammer, Clone, Create-a-Style and Storage. Pick Storage and select the Collection Helper It should have then been taken to the Family Inventory.
After that, press X and access the menu for Buy, Build and Family Inventory. Chose Family Inventory. It should be the third option. Find the Collection Helper and at the bottom it should tell you things like Y=Sell, A=Select, X=Move. Press X and it should appear in you personal inventory when you get back to live mode.