RE: Buying a Marathon...
I can't help you on finding a good deal, but wanted to point out the Marathon isn't rated for as high a weight in Canada as it is in the States (or at least that was the case when I was shopping for them). I didn't know that when shopping for a new seat for my large 2yo this summer, who had outgrown his Evenflo Triumph by both weight and height and needed a combination booster of some sort - he's already just shy of outgrowing the limits on the Marathon at 3yo.
I think it was rated to 45ish lbs for FF, so it didn't make any sense to get it when the Evenflo Generations combination booster was rated to about the same weight harnessed and 20ish more lbs as a belt-positioning booster, and was several hundred dollars cheaper.
HTH!
eta: details - sorry for being confusing and vague the first round!
Petra
Mother of Two
Owner of BaDumBums