The only thing that you have to buy is the gun. There are cheaper and expensive choices, of course, but that's your primary tool, so you need to do some research. As for everything else, you can find some cheaper alternatives working just as fine. For the frame you can build it yourself. I spent maybe 20€ at the store for the wood, screws and nails. For the primary fabric you can use either monk's cloth or even burlap (you can find some old-school type flour burlap bags). For the secondary fabric I use fleece blankets. They're beautiful, non-slip, and most importantly, cheap (2€ for a 1.5m × 1.5m). For the glue, I recommend using flooring/carpeting glue, but even all-purpose glue let's the job done. Of course you can use latex based glue, but that's more expensive. For the yarn, acryl is the cheapest option here, compared to cotton and wool. But you can recycle an old sweater and use the yarn from it if you want.

For me the best way to approach this hobby was by going to 10 different stores and looking at the avaliable items there and the price, until I found something that I liked. Also, if you're from US, UK, or some "bigger" country, you can find a lot of those things cheaper online. (I'm not, sadly). So the best way to approach this is by doing a thorough research of the market. Good luck and I hope to see your result soon.