place to make a 3D chart with a formula?

The viewer itself (http://www.dpgraph.com/graph-viewer.html) is actually free. It isn't that complex to use, but if you want you can use Wolfram|Alpha or Mathematica to produce the charts as well (albeit the latter costs money).

i tried using the viewer, but when trying to change stuff in it it told me that i needed to pay for the other version to be able to change formulas.

and i tried wolfram, couldn't get it to work, aaaargh, i feel like giving up ._.

just as example, the chart i'm trying to make would end up looking kinda like this:

 Spoiler

checking the site from which i got that picture, might have found it, dunno