I must flatten (not necessarily level) an uneven concrete floor, 25'x15' in order to receive a floating laminate wood floor (Traffic Master Dimension). I imagine I'll have to do some grinding of high spots, but I'm most concerned about filling the low spots. SLC products sound scary difficult to work over such a big area. Also ghastly expensive. I'm volunteering this work in the home of my missionary sister. This wonderful woman has had the flooring in boxes for 10 years. Her husband is too crippled up to be able to lay it.

I've heard of using roofing shingles to level where a hardwood floor is to be nailed over uneven wood. Are glued shingles an option here?

I need a solution that is easy, quick and cheap. But barring that, one that is at least doable! Thanks a million.

Your best option would be a pourable floor leveler and I definitely would stay away from wood shingles as shims on a concrete floor, they will rot quickly