I'm currently using my third weighted blanket. I think that weighted blankets are awesome and everyone should know about them. My weighted blanket is so important to me. People question me carrying a 20-25 lb blanket when I travel but it matters.
My first blanket was queen sized, second is full but isn't as nice of material (I still have this one but am not using it actively, it makes me sweat), third is my twin sized one that I have for travel and for when I need heavier weight per inch.
I use more than the recommended amount, but recommend to others to use it unless they know for sure they want more. Be careful - there is a maximum safe weight to sleep with - its 20% of your body weight.
The 10%+ 1 lb though is recommended because it is the best for most people. My first blanket was based on that ratio, my second was as well. Most people I know use that ratio happy, most people my OT knows use that ratio happily. It's recommended for a reason. Some people need particularly much, and you know if you're one of those people, its not needing weight, its needing a lot of input, that is when you go above that. (I'm the type of person who wears a breast binder for the propioceptive input, a weighted vest over that, and then wraps up in my weighted blanket on top of that.)
Oh, also 10%+1 lb is for a twin size - if you get a bigger blanket, get it heavier is what I'd recommend. Use the ratio, 10%+1 lb: Twin size = new weight: new size, to figure out what you want (So (10%+1)/twin size)*new size=new weight). I did that for a queen size, which meant I got the same amount of weight per inch for my queen size blanket and if I needed extra weight I could fold my blanket in half ontop of itself and get two layers. I thought that was the best even if it was awkward to double up like that.
I really like just straight poly pellets nothing else for fill. Poly pellets + polyfill is a good option depending on what you want sensory wise. I highly recommend poly pellets for the weighting. Some places use glass pellets and I really didn't like what those did for me sensory-wise. Anything besides those options will make a lower quality blanket - one which you can't wash as well and/or one which will break down faster.
Just poly pellets would mean you can feel the pellets, polyfill would mean it'd be puffy and feel like a normal blanket but heavy. I like feeling the pellets moving and getting to fidget with them with my fingers, and how they move against my body. Other people prefer it being a puffy blanket that's heavy. That's a matter of preference. I've used blankets of both sorts and find them both good quality blankets. I just know which I like better.
Cheapest way to get a blanket is if you or someone you know makes it for you. My first blanket I made, my third blanket my boyfriend's mother made. Otherwise, yes they are expensive. I find it worth the money without a question.