If there's one thing I'm certain about is that 'the price' is the price to use the Eluvian. Solas clearly wanted to use to orb in some manner, just like Cory did. When Cory couldn't use the orb he went after the Eluvian. So it's not pretty solid assumption that now that the orb is destroyed, Solas too is going to use an Eluvian for his work instead.
It was also partly Solas' fault that the orb got destroyed so he should be the one paying the price to use the Eluvian. But instead of him it is Flemeth who pays the price by giving up a part of her soul /dying /whatever she does, because apparently the 'people' need Solas, meaning there is something he can do that Flemeth cannot (why?). What this 'thing' is is something we will likely find out in the future games.
All that remains to be seen is whether Flemeth is truly dead and gone (something I find very very unlikely) or is she just making a fool of everyone like she did after DAO.