As most painters out there know, it can be expensive to keep a collection of paint supplies. Luckily, there are ways to avoid undue expense. My first suggestion is to purchase paints you can use more than one way. I like to use acrylic for washes and solid contrasts to add different styles and textures. Washes can give a more “watercolor” feel without having to switch mediums, and allow for on-canvas color mixing. I also like to mix acrylics with other water based or alcohol based mediums, like Sharpies or Copic markers (Sharpies will bleed more with water than alcohol inks, so keep that in mind). This is another easy way to achieve different textures and levels of detail without purchasing new products; you can use items you already have around the house.
Oil paints can be even pricier, which is why I recommend purchasing a small selection of commonly used colors like primaries, white, black, ochre, and perhaps a few standouts, but mixing the rest yourself. The great thing about oil paint is how easily it blends on canvas to create variety in tints and tones. Oil based paint can be used as a glaze to save on volume of paint used. If you like a thick build up look, layer old papers or newspaper to create texture and depth rather than slapping down paint. You can even shape thinner paper, like tissue paper, by layering it in strips that create the desired shape. Just like with acrylics, you can also combine with other mediums you may have that mix well with oil, like colored pencils or pastels.
Lastly, there is no shame in buying student materials, You can find many quality products at a lower price if they are aimed toward those trying to learn. It is especially important not to break the bank if you are trying a new type of paint for the first time.