Ask HN: Gifts for Maker kids

I have 3 boys (9, 11 and 14) who have all asked for various maker type presents this year.

The youngest wants Lego Mindstorms, having taken a week long course in the summer at the local rec complex.

The middle one is the artistic type and has been asking for a 3D printer for a few years, and is also bugging me to get him into electronics.

The oldest is taking a robotics/automation course at junior high school and is asking for an Arduino, sensor kits and stuff to let him make up interesting projects.

I've been doing research and trying to find good electronics/robotics kits and a reliable and flexible 3D printer, but the options are vast and time is limited.

I thought I would ask the HN community for their thoughts and experiences, as it may provide information that is generally useful for the parents in the crowd.

Personally I'm trying to keep it around $500/kid, since I view this particular round of enthusiasm as an investment in their futures, but would be open to spending more (or less!). Any opinions on options at any price point would be interesting for discussion.