Hi Darryl
Cost of living: It all depends on what you want to include in the cost. Have you got hotels/accommodation arranged? If so, does it include meals? Are you just looking for how much additional spending money you would need.
Weather: have a look at this webpage for climate info:
http://www.africaguide.com/country/kenya/info.htm#climate
the weather will be warm, maybe with a little rain occasionally - but nothing to be concerned about.
I guess you are going to Mombasa for essentially a beach holiday and want to arrange a safari from there for a few days:
Have a look at these itineraries - they can be arranged with pick up from your accommodation.
Kenya Air Safari 3 day Masai Mara
http://www.africaguide.com/travel/index.php?cmd=5&pid=181
Kenya Air Safaris-Magnificent Mara-3 days
http://www.africaguide.com/travel/index.php?cmd=5&pid=489
both itineraries can be customised to suit your requirements.
You just need to complete the form at the bottom to request more information. Please note that lodges are getting fully booked up so it is best to make your arrangements ASAP.
For all safaris in Kenya visit this webpage
http://www.africaguide.com/travel/index.php?cmd=2&page=1&country_id=24
Note: safari itineraries displayed on The Africa Guide website are operated by fully registered tour operators and you can view feedback received by us directly from previous travellers who used this website to find their safari holiday.
Hope this helps
Regards
The Africa Guide