Just to add to the malaria tablet advice... go get a jab. Do yourself a favour and avoid tablets. Apart from tasting awful and requiring to take them habitually, they come with an insane amount of side affects for a good fraction of people. Side affects can be from mild nausea/diarrhoea to severe enough to ruin a holiday. Considering the money you are putting forward, dont bother with tablets.
I can safely say that cost is not in any way a factor when it comes to my health on such a trip. I would do a jab every time rather than than risk forgetting to take a tablet one day... stuff like this is crazy to skimp on!
I went with a regular company, First Choice iirc in July/August to Diani Beach and I chose 1 week on safari. Tsavo or Tsavo East Reserve with the lodge type dwellings... no tents these but log type dwellings with mod cons. Well Mod Cons meaning big bed, shower etc but no TV, Wifi but you can do without that for a week with so much to see.
On the Diani Reef Beach Resort and Spa week I went on a reef snorkelling trip and saw whales which was a massive bonus. I even managed to get shots on my camcorder despite the boat rocking as everybody dived into bags etc to get cameras/camcorders.
Mod cons sounds good... was there an epic mosquito problem? Also was it dry heat or humid heat... guessing dry?