I just paid $150 for a good used 21" tube, it wasn't a correct Predicta tube but one with a longer neck that will sub.
I wouldn't hesitate to ask that much for the strong 17" tube on eBay, given what the Princess sets are selling for.
You can always take less if there are no takers.
The lesser tube maybe $25-$50 if it's useable.
VK members should be offered a substantial discount of course.