Mosaics and collages can be done with household materials or an inexpensive kit from the dollar store.
The Simple Start in Chalk Pastels series from Hodgepodge is inexpensive and looks very simple. She even has some youtube tutorials to go along with them.
As for sketching, you can check your library for simple drawing books. If you have the TBN channel, you can catch Mike’s Inspiration Station on Saturday sfternoons, as well. Neither of these options would require expensive materials, just pencil or marker and paper of any type. Super simple and super fun!