How do I place my camera on uneven surface without spending too much money on equipments.
Rocks is one example of uneven surface.
To a large extent, this depends on your camera (and lens), how uneven the surface is and what you mean by "too much money", but the obvious answer here is a Gorillapod or equivalent (other brands are available).
I often got away with using the camera bag and/or the lens cap. And small objects (rocks) around can be moved as well. For shutter speeds up to a second, I also lean my camera against poles or walls, locking the hand grip against it. For time lapse you probably don't care so much for long exposures, you just want no motion in between successive exposures. Then you probably get away with the cheapest tripods around.
Molding a chunk of clay onto the surface and then putting something flat like a small piece of wood on top to balance the camera on could work for a variety of surfaces.
The clay would need to be relatively stiff though so that it does not deform under the weight of the camera.