That is going to depend primarily on the number of climbers in your group, the route you take (3, 4, or 5 nights), and your reliance on porters. The math can seem complicated but here goes:
15 months ago I paid about $550 to go up alone with my guide (John Mukuruma) and his porter friend Graham. We took the quickest route up and down (Sirimon) and did it in 3 nights. I guess that taking inflation into account, that would be about $600 now.
However, I booked the climb through an agent who I believe took quite a big cut of the money (how much I'm not sure). If you want to contact John or any other guide directly, you can realize some savings. Everything of course depends on your bargaining skills. You may well be quoted an even higher price to begin with but bear in mind that they are seeing you as a newbie who doesn't know what to pay.
The good guides deliver a terrific experience and I feel they should be paid well. That is another reason to book directly with a guide: the money you don't pay the middleman should in some part end up in the pockets of the men who actually take you up. (I have a suspicion that my lady agent didn't pay the staff all that well.) If you are a single customer, I think 3,500 shillings/day is the minimum reasonable rate for a guide and 2,500 for your porter - that is just my feeling, and bear in mind that they don't work every day. If you have friends along, the guides will definitely demand more but it will work out to less per climber.
A word on porters: They are not absolutely necessary and you can always carry your own pack if you are very fit. But a porter frees you to enjoy the trip more, take photos, etc. However, on no account do you need more than one porter per climber, at least if you are just doing the "easy" Lenana Point summit. You shouldn't let yourself be talked into taking on more porters.
So much for the human component. Now you add in the Mt. Kenya National Park fee. If you go to the KWS website you can see the fee packages for the different routes, but it works out to around $60-70 per day. You also need to cover the entrance fees of your guides/porters, which are fairly token as they are Kenyan citizens. The sleeping huts are US$10-12 per night for foreigners and around half that for the Kenyans.
Foodwise, I think they budget 500-600 shillings per day for your European diet, less for their own Kenyan food that they love so much. Finally, a few dollars goes for a jerry of kerosene that the porter hauls up to the huts for cooking.
All the major staging towns for the mountain can be reached from Nairobi by public buses. From there, you can opt to have a taxi take you to the gate (around 2,000 shillings I think) or just get on a cheap motorbike taxi like I did. Again, scope here for savings.
I hope this helps you in your calculations and negotiations.
