Hi Darvio, it sounds like you want somewhere warm and outside Australia? The best place will depend on what type of windsurfing you want, and the $$$ travel budget - travelling solo or with family? - waves or flat water? Are you ok doing other stuff if no wind or do you only want a windy destination.
Mauritius is way more $$$ than Maui, it's mostly all inclusive resorts, although you can find cheaper accomo,, the windsurfing conditions and wind reliability in June in Maui is much better than Mauritius. Maui is not that flat in June, (search on GreenLeader Cold and Windless posts), there are waves and wind swell to be found if that's what you would like, Flights to Maui are cheaper than ever, but you need a car.
How about Fiji ? Formula Nova loved it there