I was a ninja turtle in high school. My dad decided the costumes in the store were pretty lame so they got me a green sweatshirt and sweatpants and he made a shell for it that one of my cousins borrowed later.
As a mom, years ago I watched Edward Scissorhands with my boys and the eldest wanted to be ES for Halloween but of course there just aren't many costumes out there for 5 year old boys for that character. So I got him black pants and a black turtleneck, some black ribbon and two metal bobbin rings. I attached those to the shirt and then got black knit gloves and traced scissorblades onto cardboard, spray painted it all with silver paint and sewed them onto the gloves. Painted his face white, used eyeliner for the "scars" and such and though he's blond with thick hair (or it was blonde back then) I got some of the temporary color spray and tried to blacken it up.
The year my middle child went as Harry Potter really kinda soured me on buying costumes. For about $25 all we got was the cape. We had to then buy the glasses along with a tie for $10 apiece. And I had to get him something to wear under that would look like a uniform. We try to either recycle costume pieces or I buy stuff at thrift stores.
In 2012 I threw together a Barnabas Collins costume for my oldest son while my middle son wore a black shirt and pants with a cape and a shirt bunched up and under his shirt to look like a hump and I wrote "H. Delbruck" on his palm and told him to switch the hump from side to side. Last year I got a yellow shirt and sewed a black zigzag stripe onto it so he could be Charlie Brown.
And in 2012 I made the little one an Animal costume.