Programmable robots for children

A few weeks ago my son attended a summer day-camp where they played with various kinds of robots. If I understood him the most interesting was the LEGO Mindstorms and of course he wants me to buy one for him. The problem is that it is very expensive (280 USD in the US + shipping)
or I might be able to buy in a local store but then I am sure it will be around 400-500 USD.

Besides the programming environment runs only on Windows and on Mac and we run Linux at home and only have Windows in a VirtualBox.

So I was wondering if there are cheaper alternatives, at least till I see that he is serious in playing with those robots.

Hard to get started on Dreamwidth

I guess, I have not yet figured out how to use DW.

I know how to post to my account, how to join a community and how to post to that community but I don't know why?

I mean I don't see a point in writing - especially asking questions - if there is no one reading it. So how can I get people read my entries? I tried to look for some ideas, maybe a dw_community that deals with this question but I could not find one. I found the list of official DreamWidth communities but the closest I found to what I am looking for was
dw_community_promo and maybe dw_nifty but neither is really what I want.

Maybe the problem is that I don't know anyone here. Well I know csjewell who invited me
here and I exchanged 2 e-mails with damned_colonial but I don't think I know anyone else here.

So how do I get knowing others here?