Ann: Rett Syndrome NDA accepted for Priority Review by FDA, page-26

If I remember well, Little T has put that figure at around US$150M or more plus the internal cost which is not negligible.
IMO, and I posted my preference on other thread a bit earlier, it would be more prudent Neuren to licence the US rights to a big pharma (an identical deal to Acadia's) and let them pay and run the P3 trials and deal with FDA in the subsequent approval process. A big pharma would have money and employees' manpower to deal with 3 or 4 large P3 trials (probably recruiting 180-200 patients each). The cost of the trials is significant money and the initial cost calculation can easily blow out (look around at cost blowouts in every area of investment these days). It's better to be more prudent and share the pie before a P3 trial (rather than greedy and uncertainty of trials real cost) and hopefully, Neuren's board share my opinion.

And YES, they can negotiate a better deal than Acadia's saying at the negotiation table they can the run the trial themselves, but not do it in the end.