SWMBO and I do couples costumes on the cheap and/or DIY.
From recent memory.
This Year (2 parties, 1 down one to go) I'm Bob Ross, she's a Happy Little Tree, see Slefain's description for Bob, she wore all brown and had branches with leaves from Hobby Lobby sticking out of her hair.
Last year we were Fry & Leela from Futureama, I made a Planet express delivery box, Slurm koozie, and bought a red jacket from eBay. She got a purple wig, toy ray gun, some cheap boots, and we made her wrist communicator and eye from craft foam, everything else was from our closets.
A few years ago I was Indiana Jones & she was Short Round, thrift shop for clothes, party store whip, and "Freddy Krueger" hat I modified, already had the jacket. For her I used a blue paint pen and ink jet iron on NY Mets logo to turn a cheap plain white hat into a vintage Mets hat for Short Round, clothes came from thrift store/salvation army.
We were Paulie Bleeker and Juno from the movie Juno, ink jet printer iron on Dancing Elk Condors logo on a burgundy Hanes Tee shirt from Walmart, dyed some white sweat bands yellow with Rit, borrowed some yellow shorty-shorts from roommate's girlfriend, already had tube socks and tennis shoes. Juno was thrift shop clothes, died some shoe laces for the Dr. Martins, and a balloon for the "preggo eggo."
We did gender-bender Sonny & Cher once too, I make an ugly woman, and she looked more like Groucho Marx than Sonny, but it was all thrift store/Walmart clothes. Finding an evening gown that fit was a challenge.
The Bandit & Frog, red pearl snap shirt from eBay, already owned the hat, fake mustache, kick ass belt buckle from eBay, already owned the boots and jeans. She got her hair done, "feathered" like Sally Field's, and got clothes from thrift shop.
I know there have been others, but those are what come to mind right away. We never spend much on costumes and always do well in the contests, got 1st place with Bob Ross & the Happy Little Tree last weekend. Got 3rd as Fry & Leela.