I was always told not to use flea meds for dogs on cats, so I buy for both the dogs and cats. I just don't want to take a chance of giving the cats too much of the stronger dose that is specified for dogs only!
Advantage or Frontline is best and you can get that at a reasonable price thru drsfostersmith.com and they do ship international also.
Also being that you are in a warmer climate, you probably should start using it year round. Once you get rid of the little nasty critters on the animals and in the house, you shouldn't have any more as long as you stick to the once a month schedule.
Good luck!