Got mine undercoated yesterday at Rust Check on Bloor St in Oshawa, Chris does an amazing job, (I use to do my own so I know a good one from a bad one) It took him almost 2hrs and the truck is completely covered, not one dry spot anywhere!
I also just got back from having a Pendaliner box liner installed in my truck.
$199.00 at Action in Whitby, which was the cheapest around that I could find. (just wouldn't buy much else from them however)
I have had a box liner in my P/U's since I was 16 and not once has my box rotted off or rusted through.
I do however spray underneath it every couple yrs with Rust Check and I have always had a Tonneau cover so I assume that helps, but paying $550.00+ for a spray in liner just doesn't make any sense to me.