Hello, Marillia!
I'm excited to hear you've made plans to run your first half marathon with
runDisney! Every mile is magic and I have no doubt you'll have a great experience.
When it comes to planning your race day costume, I highly recommend you purchase your desired attire prior to the race. I would also make sure you wear it on a training run to test for comfort. Nothing is worse than getting halfway through a half marathon wearing something new for the first time, only to find there is major discomfort or chafing issues. If this happens, your race experiences might not be very magical. In addition, you may get to the Expo only to find your desired size, color or preferred fit is no longer available.
You'll also find at the Expo there are not pre-made costumes, but rather vendors who sell graphic t-shirts and other various running gear. For a full running costume look into Esty & Ebay for talented vendors who can hand-sew a running costume for you.
Need running costume inspiration? Check out the
Running in Costume Series on the runDisney Blog. It's sure to give you some great ideas!
I hope this helps, Marillia! If I can be of any further assistance please do not hesitate to ask.
Happy Running!
Faith