We are all in college and on a budget. We found boxes at the local hardware store and spray painted them and added foam wheels, numbers, and string to attach to our body.
For Mario and Luigi we bought mens suspenders, colored tee shirt and base ball hats, we super glued foam letters on the hats and wore white gloves as a final touch. Princess peach wore a dress she owned and made large jewelry out of sticky back foam paper. For Waluigi we spray painted salvation army snowpants purple and bought a fake mustache from a quarter machine. Bowsers costume we took a garbage lid and attached string like a back pack, we put a pillow case over the lid then stuffed a pillow in to make it puffy. Then we spray painted birthday hats and hot glued them on for the spikes. He wore yellow sweat pants and a yellow shirt and spiked his head with red paint.
Yosho's costume was the hardest to come up with. We bought a kermit hat from walmart and then took an old green graduation gown and tied the back to make it look like a tail. For Toads costume we had her wear a blue shirt and white shorts. We took a soccer ball hat we found at the dollar store and put red felt polka dots on it.
We had a blast with this Homemade Mario Kart Group Costume and even took our karts in a cab to the bar.
We decided to do an easy group costume with Mario, Luigi, Wario and Waluigi. We found men's tshirts, gym short and white leggings in the colors we needed. The we found matching tan hats and dyed them ourselves. We took color duck tape to create fake suspenders (Waluigi's is backwards). We cut float paper for the hat symbols and yellow buttons.
Since this was a 1/2 way to Halloween party we couldn't find white gloves but it would have been a nice touch. Over all this Mario Bros Group Costume came together nicely.