If it were myself and you could work your family into a 2500-3500 Crew Cab truck it may save some money. Up here the Suburbans and Excursion's are hard to find and when they do they go for about retail. However because of construction / slope trucks you can find a 3/4-ton or 1-ton in Ford / Chevy for pretty good deals.
I have test driven the 8.1 Suburban and it has some serious power behind it, but I wouldn't exclude the 6.0 for what weight your carrying. Same goes for a 5.4 Triton with 4.10 gearing if you can get a screaming deal on it. The "perfect" towing vehicles with correct motor + gearing go for a lot more because the owners know what they have. The small block 5.4 / 6.0 with 4-speed or if you can swing it 6-speed seem to be a lot cheaper in the price range but still allow a lot of towing.