Here's the thing with Deion. Jerral is a marketing guy first. He's going to look at how much money he will make with big ticket Coach Prime on the sideline. It's reasonable to say TV ratings and merchandise sales would spike, at least in the first two or three years regardless of the performance on the field.
JJ subscribes to the Elvis mentality of "all publicity is good publicity". Bringing in a polarizing figure will have people tuning in to see the product. You'll see new viewers that are curious to see the circus. You have the long term fanbase, us, that wants to see the team succeed. You'll have the haters that want to see the team fail....but then you add in the Coach Prime fans and haters, and there are many. When you add ot all together, is an $8m buyout really an obstacle? It's likely that Jerry Jones is considering whether the added publicity and viewers would offset the buyout, as well whatever contract numbers Deion is looking for. If he succeeds, and I do think he can, any sort of long term relationship is a massive win for the Jones clan.
This is a move that could pay for itself, and Jerry Jones knows it. It's definitely something to keep an eye on.