Found this tip in Real Simple magazine:
August in the best time to buy a swimsuit! Some websites, like victoriassecret.com and everythingbutwater.com will have abundant inventory that’s on sale. You can update an exisiting suite by picking up a new top if you already own coordinating bottoms since many suits are sold as separates.
Hurray for sales!
If you can’t buy now wait until May when retailers will slash prices again.