I can completely relate to your hesitation about buying these, simply from sticker shock. Personally I love makeup and I'm not a "pro" but do it enough that I wanted to invest in good brushes. I ultimately wanted MAC, but those range from $20-$60 per brush. If I had gone with MAC, I would of spent about $500, and I know their products are amazing, but I couldn't spend that much.
My honest opinion is that these brushes are great, and to me were totally worth buying. They're vegan and made from synthetic hairs which help if you're prone to breakouts since they don't carry as much bacteria. If you think about it, you're getting 12 brushes for $120, that comes down to $10 per brush. In the end it will be your decision. I'm pretty sure Sigma offers returns if you're not satisfied, and you can check to see if there are any coupons online. I got $10 off my order (which covered shipping) and a free mini eyeshadow palette. An over the counter brand I like are EcoTools.