I'm not sure what you mean by big expensive kits and lower level ones. LEGO Education just came out w/ a WeDo kit which is a scaled down version of the LEGO Mindstorms NXT. You build things, and program them using the computer but it stays tethered to the computer so there is no NXT brick for it to go out on its own. The WeDo runs about $120 compared to $250 for a LEGO NXT kit.

If want some science LEGO kits, check out LEGO educations Mechanisms kit and MOtorized Simple Machines kit.