Last September I ran Dumbo Double Dare (10k on Saturday and a Half Marathon Sunday) To run 19.3 miles was challenging but the dressing up part helps. I did a Belle costume for the 10k. What you need is a yellow tank top, some yellow fabric about 2 yards that you will cut, fold and sew together, and a rose if you wish to add it. I found a yellow tank top at Forever 21. I bought yellow fabric at the fabric store. I sewed the fabric in one long band.
I have a simple Singer sewing machine. You don’t need anything fancy, you can even hand stitch the fabric. Then I hand sewed the band to the tank top and sewed on the rose.
I then cut some old opera length gloves and dyed them yellow. I bought a yellow sparkle skirt from Sparkle Athletics, there are tons of running skirts you can buy or you can make your own tutu. I will try and make one and have a tutorial on how to do it eventually.
Here is the 10k Medal I got for running 6.2 miles. Pretty cool medal.
Hope this inspires you to run a race in costume.