I'm quite interested in small rockets-balloons that can reach more than 50km, 
thus I want to build one myself (With my school financial support). I just want it to carry like a 350g-450g equipment. My aim is to make some really high quality footage up in there. I (almost) get that a meteorological balloon would be quite ideal, but still, it just wouldn't be original to vindicate the investment.
That said is it even possible to make it for under 600 dollars?

I'm also not sure about the availability of the things since I live in the central Europe