Do you know how to sew? It's possible to make a weighted blanket for not too much money. I personally made mine for $50, and I'm an adult so I had to make an adult sized and weighted one. Yours would be much smaller.

If you can sew (or have a friend who can, then poly pellets (which are reasonable cost on ebay), some nice cotton fabric, and time, and you get a weighted blanket ). I can help with advice as to how to do so, how much weight to use, etc, if this makes sense as to how to go about it.

Other options; It's rare, but sometimes insurance will cover a weighted blanket. With the diagnoses you have its unlikely, but you could attempt it. Usually it only works for people with autism, and only sometimes then, but its a thing you could try.

Used on ebay is generally a thing to look into for certain types of things. I'd make a blanket over getting one used, because they do wear out and because you can make them so cheap, but other things that's a great option. I got noise cancelling headphones for $25 - a solid midline pair, not Bose, but what had been Sony's top end at one point in the past. I got the headphones and some CDs for therapeutic listening (I don't know if they recommended that for you) on there for cheaper than I would be able to rent them from my OT - still a good bit of money, but some savings, and I could resell after if I needed (I have kept them because I still use them).

A weighted vest I don't have good advice for places to get. I haven't found any commercial ones that are adult sized that I like, don't know about any that only make kid sized ones. Mine was homemade for me.

However another great option for that is to look into compression shirts. Instead of weight there, you have compression, and there you can do something as simple as the athletic wear. It's normal clothing cost instead of medical cost, hard for someone low income, but easier than medical equipment and how those are always more expensive costs.

There are lots of tools for SPD, but there are a lot of ways to make a bunch of them obtainable cheaper.