I bought a black strapless floor length dress on Craigslist for $20 for this Homemade Ursula Costume. First I hand altered the top to make it cinched/low between the breasts like Ursula's top is. Then I did a bunch of measuring on the lower part of the dress and cut vertical down triangles out of the bottom of the dress, leaving 8 remaining sections hanging down that were shaped like long triangles with the pointy half cut off.
I reattached the 8 pointy triangle pieces to the remaining 8 dangling pieces, making 8 long black triangular tentacles that were longer than the original dress. I bought cheap purple fabric and cut into triangles with widths a little wider than the black strips and attached those to the black portion of the tentacles.
After the purple pieces were sewn on, I added an extra purple width to the inside of the dress and tacked it up so the individual purple tentacle bottoms wouldn't hang down and be visible. I stuffed each tentacle with poly fill and inserted copper wire in each and bent it out and up. I wore black tights and black heels.
I bought the wig on the Disney website. For makeup I did a pale face (she actually has lavender/greyish skin), blue and green eyes with the green going way above my own eyebrows, black eyebrows, a black mole, and red lips. I painted my nails red.
The earrings were shells from Walmart that I painted lavender with craft paint and drilled a hole in the top and added wire jewelry pieces to make them into earrings. I couldn't find a shell for the necklace so I carved one out of green floral foam then painted it with gold spray paint. I made a hole in the back to loop a black leather type cord through and just tied it behind my neck.
I sewed Flotsam and Jetsom (the eels) out of green cotton, and sewed in green and white foam sheet pieces for their fins and teeth. I glued on Google eyes and colored one eye on each eel yellow with Sharpie marker. I stuffed the eels with poly, and hand-stitched to close the openings where I stuffed them. I gave one eel an insert to use as a purse with a button closure (it worked great to store things like my phone, ID, and camera). I attached each eel to my dress with a button on the dress and elastic loop on the eel.
Total cost: a little over $70. I already had the craft and spray paint and the wire jewelry pieces for the earrings, but I pretty much purchased everything else.