Lego Mixels are probably the cheapest sets that Lego sell, coming in at just £3 each, for about a 60-70 pieces. They’re aimed at ages 6+, and there have been 7 series so far, with 9 sets in each series. If you can’t be bothered finding them all, Amazon have the full set.
As individual models, they’re bright, colourful, and easy enough to build even for younger hands. Noah managed one of the sets by himself, so the instructions are also easily enough to follow. The series breaks into three groups, police, medieval and music and the sets in each group can also be combined into a larger model. They’re all fun little creatures, with movable mouths and posable arms and legs,
Disappointingly, the larger models don’t actually use all of the pieces in the group, and you’ll still have a fair number left when you’re done. Not only does this mean you’ll miss out on the satisfaction of the table in front of you being empty, but it also means you’ll need to properly store the remaining parts if you ever want to build the separate models again.
Out of the larger models, Noah preferred MCPD Max, because you could open his mouth and put a minifig into the jail within his stomach. He was happy to play with all of them though, and the ball joints holding the limbs in place means that they’re strong enough to handle that.
Ultimately, it’s hard to complain about sets that are this cheap. These are pocket money toys, and far better than most things in that category.