From what I can make out about it, it appears the 350,000 is the projected price of such a build. The kids have put together ideas of how it should be & what would be included, they've then spoken to various companies & suppliers to find out what is available & feasible, the idea was then put forward in a project (I assume alongside other Schools ideas) & theirs was deemed the best option & as such the project winner, apparently this goes back to earlier this year.
Eco-classroom for Accrington school (From Lancashire Telegraph)
Accrington pupils get a green light for eco classroom (From Blackburn Citizen)
Actually think the 350,000 may be a misprint 35,000 sounds more likely.