Hi Cath5,
I've been to Cuba, but in November, so can't advise you on August, sorry. The time you want to go to that region is hurricane season, so you would be taking a chance ;) However, Cuba is a fantastic country and if you are going to go, do it soon before it all changes when Fidel Castro dies.
One thing I would recommend is to get off the resort as much as you can - the country has to be seen to be believed. We didn't go to Havana, but we went to Santiago de Cuba, the second city, and I've never seen anything like it in my life, absolutely fascinating. We stayed in a five star resort, all inclusive, and it was absolutely fabulous and exceptionally good value for money. The staff were brilliant, so warm and friendly, and happy to tell you all about their country and the lives they lead. Your budget would see you far in Cuba and you would be able to get a super holiday for it.
We also swam with Dolphins, visited a cigar factory (one of the girls working there winked at OH and made his holiday, LOL!), went on an ancient steam train and went deep sea fishing, when we got the entire boat, two crew and a guide to ourselves because no one else had booked it

And we came home with Che Guevara T-shirts!
Would recommend it, if only to experience a country that is so vastly different and unusual.
HTH
Lesley