Yasmine Hammamet has some good hotels, we use the Iberostar Averroes (right on the beach) or the Belisaire across the road. Cheap and if you go out of school holidays they shouldn't be too overrun.
Croatia is one of my favourites, but the money just doesn't go as far.
Have you considered Bulgaria at all? We've been skiing there last week and it was so cheap! For summer resorts I'd suggest Nessebar or Sozopol, there are some good, all inclusive hotels available.
GG x