Which inexpensive software do I need for converting point cloud to g-code?

Where are you getting the pointcloud? If its from the digitize wixard then you can get that to output X Y and Z moves by going to Ports and Pins and then Mill Options, you can then choose to "Add Axis letters to coordinates"

Hood

I understand what you mean, but I don´t think this will give a smooth surface and compensate for tool form and tool diameter.

You would have to edit and add tool comp but if your digitizing was small enough then it would give reasonable contours but may depend on the accel of your machine whether it would be too jerky in the many small moves.
 There may be  software that can take pointclouds and convert to code in the links section at the top of the forum, sure I remeber Rhino can create solids from pointclouds so if you had a 3DCAM it could use them.
 As for

As I mentioned to you at Cnc Zone, you can use MachCloud to convert the point cloud to an .stl. Then, use something like MeshCAM or vectric's Cut3D to get your code from the .stl.

when i tried to open an stl file in meshcam I got this error message:

ASCIISTL Parser Error: LINE 1:parse error endsolid MachCloud
Couldn't load files as ASCII STL.
Open failed.

What is wrong?

Do I need to convert something in machcloud before i save it as a stl file. When I save the files as stl, the files doesn´t show more than a few bytes.

I think you need to mesh it first, using either option under mesh menu item.   Delauny or ball set, either one.  This creates a mesh grid that can then be saved as a stl.