Not read the full thread so unsure if this has already been mentioned but went into Hobbycraft and they had huge pirate ships and land rovers in cardboard which you colour in and then build, massive boxes. They were reduced to £10 each and looked like an excellent 'big' present for younger children. There were possibly some more girlie ones but I didn't look that closely.
Also The Spicery have slightly damaged 'How to be a Curry Legend' kits in their sale at £17.48. Full price at present is £34.30 and although I know they tend to often have an offer before Christmas I looked back and even with the offer paid £19.90 for one for my dad 2 years ago. It says the tins may be slightly damaged so I ordered one for us to try at home and in has the smallest dent you've ever seen so would have been perfectly presentable as a present.