I have been painting, as a hobby and commercially, for approximately 10 years now. I first started with acrylic but have more recently dumbled in watercolors. I have always loved texture in my art work but could never afford to buy oil paints. I consider myself quite a resourceful person and this has led me to think out of the box. I will hopefully enlighten you as to some of my more creative ideas which you may want to incorporate into your own pieces.
Before I start I apply Gesso primer to my canvases. This assists with ensuring any medium added to the canvas adheres well.
I have found a product called "Decorator's Caulk" which works as a great way of adding texture to your canvas. I buy trade tubes which can be fitted to a "Sealant Gun" and this is the tool I use to apply the caulk to the canvas. From there you have to let your imagination take over. I use a large pallet knife as well as various other tools to manipulate the caulk across the canvas.
The caulk can be found in all trade shops and is not a specific art product. It is typically used to fill gaps and cracks in walls. It can take up to one one hour to dry but this will depend on how thickly you applied it to the canvas. I just touch it light and you can tell when it has hardened. You are ready to paint over it. You will find acrylic paint sticks to it with no fuss. The result is awesome and you have the perceived texture of an oil painting but at very little cost.
Crepe paper is a cheap and interesting way to add texture. I usually make a solution of PVA glue with some water to assist with sticking the paper to the canvas. Again your own imagination has to come to play here and depending on the look you want as to how layered and textured you want your piece to be.
Plaster of paris infected crepe bandages. These are a tad messy to work with but the results can look fantastic. I find that rather than trying to achieve a perfectly smooth finish it can look great if you leave it rough and if not all of the bandage is covered with the plaster of paris it adds a mottled porous look which is spectacularly organic in its texture.
Rope of all size and thickness can add a really great three dimensional quality to your piece. I use decorator's caulk to stick it to the canvas as not only does this act as a great adhesive you can also paint over it quite easily.
Cutting into the canvas. I know this sounds like a cardinal sin but the results can be quite spectacular. I have created many industrial looking pieces by combining rope, netting, plaster of paris and by cutting into the canvas and bending it back upon itself you can achieve a very raw look.
These are just a few ideas which will hopefully fire up your imagination and assist you with trying out different materials. I am sure your artwork will take on a whole new look and feel with the added bonus of very little cost.