Hi Dave,
Sorry I can't remember exactly what I paid. I organised it directly with David -but he is a hard man to get hold of. I initially bombarded his mobile with text messages & eventually he phoned me (in the middle of the night -whilst I was still in the UK) -we struggled to communicate by phone due to my thick Scots accent but I eventually managed to arrange a meet at our hotel at the start of our first week before we went off on safari.
Everything I arranged with David happened as planned or better.
I think he charged £25 for a half day -which with David can be 6-7 hrs!!

. I remember thinking it was very cheap for the effort he put in & for the results we obtained BUT you will need transport over & above this as he doesn't have his own vehicle - I think I paid £40 for a vehicle/driver over & above David's half day rate -the full day rates were pro-rata (with a 20% reduction I think-????). What I do remember is that I took £500 on the holiday to cover all birding costs but ended up using some of this to cover my son's diving costs. I was so impressed with David that we met up for lunch before I flew back home & I gave him what was left of my 'birding fund' (£80-£90) -all in all I did a full days birding @ Sabaki, a late afternoon at Mida Creek (July/August is the worst time of year for birding here but I still saw plenty of good birds), a day & a half at Arabuko-Sokoke (the half day was 7am -3pm!!!) & an extra evening at A-S for the Scops Owl. Though I can't remember exactly I think about £250 covered all this (including entry into A-S forest which is a National Park) -but of course most of that money was for covering the transport costs with David's take being under £100. To put things into perspective his rates are significantly less than Gambian bird guides, his bush skills much better & the birds are in a different league.
David knows the A-S forest like the back of his hand as do his colleagues Willy & Albert. If you struggle to contact them before you leave for Kenya try to organise your holiday to free up time for birding nearer the end (in the 2nd week if your going for two) as it is fairly easy to contact at least one of the Spinetails guys by phone whilst in Kenya & usually one of them will be available to take you out -as mentioned above transport is the big problem however.
Re Mida creek -I didn't bother with the boardwalk -I just went onto the mud & got pretty dirty -it was great! Going in Novemebr you should see lots of Crab Plovers as well as other good Palearctic waders & supporting cast. Our trip to Mida was initially problematic as the transport 'packed-in' so David & I flagged-down a bush-taxi -cramming a 6ft 3in 18 stone Scotsman with a ton of photo-gear into a minibus designed for 11 but already seating 18 was quite a feat -it ony cost about 10 pence to make the 30 minute trip so perhaps a bush-taxi from Kilifi to Mida is the answer -just make sure you leave a half day in advance.
Re seeing Sengi -if you can get to the 'gallery' forest zone just after first light then you should see them -they are absolutely fantastic creatures but are very difficult to approach closely.
My time in A-S was simply a series of photo-opportunities with new birds coming thick & fast. My first priority was to get a good look at each new bird followed by a record shot & then subsequently repositioning to try & get reasonable quality images. We saw far more than I got images of -eg Four-coloured Bush-Shrike, various Greenbuls, Fischer's Turaco, Narina Trogon, Thick-billed Cuckoo, Spotted Ground Thrush (poor view), East-coast Akalat (poor view) and brief views of Southern Banded Snake-Eagle & African Crowned Eagle (very brief glimpse & saw the nest). I did get the feeling from David that I had been very lucky as we saw far more in a day & half than I ever dreamed of but it also seems that July is a good time for forest birding in A-S.
I'll try to look out my old notes for the trip -I may have scribbled down the exact costs somewhere. If there is anything else I can help with please feel free to ask.
Cheers,
Steve