Here's an idea to improve the chances of selling Rory & River in significant enough numbers,
Basically make the first 6 figures a Build A TARDIS wave eg,
11th Doctor with TARDIS roof plus other accessories
Amy Pond with TARDIS base plus other accessories
Those 2 are the safest characters as far as people being willing to pay out top prices for so it makes sense to fill out the packages as much as possible.
Then with Rory & River make them "bare bones" in terms of accessories and just have a TARDIS wall in with each so the overall price would be cheaper than the main two.
The final 2 wall parts could be included with whichever baddies from the series are made......2 different Silents would be a decent choice as money could be saved with the attire
Accessories for Rory & River could possibly be made by our friends at WGP so there'd be no conflict of intrest.