Just thought I'd put this on for anyone thinking of going. If you go after 5pm Monday to Thursday it is only £25 for a family ticket (it's £64/£71 for a family day ticket). It's open till 8pm.
This price is only if you pay on arrival and they don't really publicise it.
We were there for some of the Hangloose Adventure activities but thought for £25 we might as well visit Eden as well.
It was great, so much quieter than it would be through the day (and cooler). We had time to look around the Biomes and the Space attraction that's on now. If we hadn't also been doing Hangloose we'd probably have managed to fit everything in. Having been I don't think it's worth paying over £60 but is def worth £25.