Grappling dummies are expensive, but if you have the money and don’t want to spend your time making one then I would definitely say buy one.
I made one about 5 years ago and it was rough and better for throws and stuff like that. I searched and searched and finally found the plans for the Bubba dummy through a patent search. It was made with wood, hose, and duct tape. It had joints but the hose made it pretty tight and not very maneuverable for armbars, arm triangles, triangles, pretty much anything. I didn’t get much use from it and was pretty bummed since I put a lot of time into making it.
Now there a lot better plans online than what I used 5 years ago. I’d say if you are a crafty person and want to make one for a fraction of the price then go for it. If I had the patience now and time I’d probably make one to get a little extra practice.
Here is one site I found. I was trying to find the plans that I used back in the day, but no luck. The dummy in this how to looks pretty good and doesn’t look like it will break the bank. Hope this helps.