I purchased all of the pieces for this costume at a thrift store (purchased all in a single trip, actually) and spent about $5. This doesn't account for glue or thread or fiber fill, since I had those things already. But if you threw those in the mix, you'd be investing another $5 or so.
The costume is INCOMPLETE as of right now (I'll explain later) but this is what I have so far, which is the majority of it. Also, please note that I am not working toward an exact reproduction of the character. I have taken certain liberties (which I will point out along the way) with the design that I don't think affect the outcome.
* purple shirt with long sleeves (mine is actually 3/4 sleeves, but close enough)
* black velour dress - this is a plus-sized, full length dress
* purple velour dress - this is a child's sized dress
The black dress that I found was stretchy and has a textured pattern to the fabric that I like. It looks more 'aquatic' to me. The neck hole actually fit comfortably around my bust, so I didn't need to do any alterations for the top to fit.
First, I cut the 'tentacles' about halfway up the dress.
I had decided from the start not to replicate the purple undersides of Ursula's tentacles. I decided to simplify (shown below), so the tentacles are just black all the way around.
Then I sewed the tentacles closed (basically like a tube) and when they were all sewn, the material had become tighter at the bottom (shown below) because the dress was, essentially, halved. Since I need to fit my body through here, I made small cuts in the fabric on the 'body' section in between the tentacles. This material is great for that, because it doesn't fray so I didn't need to do any hemming at all, I just cut and tore it until it was an adequate space for me to fit through. I then turned the body inside out and removed the sleeves and sewed up the place where the sleeves once were. This fabric is also great for hiding uneven edges, I've found! And since the sleeve holes would be in my armpits, I didn't do a great job in sewing them, I'll admit.
After the body was sewn, I attached the suckers to the tentacles. I cut circles from the purple velour child's dress and attached them with hot glue.
Before starting, I put a strip of cardboard covered in box tape inside the tentacle fabric, so that the two sides didn't get glued together. The box tape made a slick surface, so that the glue never had a chance to adhere (if I'd used just cardboard, the glue might have stuck a little to it).
I then put down a blob of glue and pressed the circle into it, using my thumb. YES, THIS IS VERY HOT. I would sometimes set it in place with my thumb and then use a marker (I had a Sharpie nearby) to push it down the rest of the way.
When the suckers were attached, I stuffed the tentacles with fiber fill. I then attached the 'body' to the purple shirt, for ease of wear. I also used hot glue for this attachment, instead of taking the time (and energy!) to sew them together.
The final product is being held up by my husband, who is also holding up one of the tentacles so you can see the suckers.
And another shot with the 'body' stretched out, so you can see how the tentacles will hang when worn.
I'm debating whether or not I will fill in the space between the shirt and the 'body' with fiberfill. Ursula is a full-figured octopus, but it may be too hot for wearing all night (the past couple of Halloweens have been scorchers), so I may just let my natural figure fill it up. :)
This is only the top 1/2 of the costume, because I don't want my legs to show at all, plus I want the tentacles to be easily seen, so I am constructing a skirt to go underneath that will represent the water in the ocean and possibly have some fish in it... stay tuned!