I use the 12" Lacks ($7 a pop) to display my CO Tardis collection. They're only rated for 6lbs max load, but that's fine for the Tardises and should be fine for most 12" figures as well.
I also have four of the 75" Lacks ($20 each) that I use for other stuff and as long as they are installed correctly and go into at least one stud (ideally more of course) they should hold up to 70lbs.
I have had good luck finding them in As Is, especially the 12" ones which is a nice way to save a few bucks.
I have to agree with Duck of Death...make sure you bolt it onto at least 1 stud.
Here's how I have mine setup right now. It's real sturdy. I even have about 40 Gunplas displayed on one of the long Lack shelf and about 12 9" Vinylmations in their boxes on another.
I recall IKEA revising their Lack shelves. I bought 2x of the 1st version and that one sucked! It's not as sturdy as their latest/current revision of the Lack shelves.