Wait. Are you saying you can get one without pre-purchasing?
Can you just walk up and buy one?
Beta_Ray_Bryan, Mattel only puts a portion of its SDCC exclusives up for pre-sale. The rest are sold at Matty's booth on a first-come, first-served basis of daily allocations. Unfortunately, you have to be there early since a lot of their previous Hot Wheels exclusives sell out quick each day. It is a lot nicer to have the pre-order so that you are guaranteed the set.
Additionally, Mattel offers many of their SDDC exclusives on MattyCollector a week or two after the show closes. Please note: there is no 100% guarantee that the Hot Wheels exclusives will go on sale on MattyCollector since technically Hot Wheels is a separate division from MattyCollector. However, previous SDDC Hot Wheels exclusives, like the Back to the Future DeLorean, have been available on MattyCollector after the show so it is likely.