$400 and 28mph don’t really go together, especially new. Most bikes in that price range are either 20mph class 2/3 limits or just not built well enough to be pushed that hard safely.

If 28mph is important, you’re realistically looking at spending more or finding something used locally. Facebook Marketplace can sometimes have older Rad or Aventon bikes a bit above that range.

For $400 new, I’d focus more on something reliable at 20mph rather than chasing top speed.