Awhile back, I made a pair of jammies for my daughter, from two of my husband's t-shirts.
I love the way they came out!
For the top, I used a vintage t-shirt pattern that I found at a thrift store. For the bottoms, I traced around a pair of leggings that my daughter had. Then I added hearts to each piece in contrasting colors! They kind of curl around the edges, and I like that.
The pattern cost $.10, I had the elastic, thread, and of course the t-shirts. One pair of jammies for $.10 is not bad at all! :D