Looking online, it appears that Gigawatt hasn't been officially "released" for pre-order yet anywhere.
If any online store has it listed, it is just speculative based on what the Walmart edition cost, to lock in people before they see it elsewhere... as we still don't have an official box image of the regular edition released by Hasbro yet.

I'm not sure what the wait is for, as it is expected to be released at around the same time as the other crossover toy Maverick.
(It would be good if it wasn't yet produced, and it was being delayed for them to rework that horrible windshield, due to the backlash over how it looked.)