I just took my boys (1 large dog, 1 cat) in to start the process.
Total vet bill: $134
That included:
- $20 fee to even look at the animal (each)
- $48 microchip for the kitty (he'd been chipped before but it couldn't be read so he got a new one)
- $18 each for rabies vaccine (they were current and won't expire until 2011, but just in case...had to do the kitty anyway since you have to do the chip and then the vaccine, so he needed a new vaccine post-chip. Figured the pup may as well get one, too)
- $5 each for "biomedical waste disposal" (the needles for the shots, I guess)
I'm going in next week to do the blood draw for the KS test...I'm estimating it'll be ~$150 or so for both pets, depending on how much they want to charge me for overnight shipment to KS.
Turnaround time on the titer from KS is around 3-5 weeks, apparently, with 4 weeks being the most common. The clock, as you say, starts ticking the date of the blood draw, unless the titer test fails, in which case you have to re-do the vaccine/test. (So my appointment next week is on 6/11, so my boys should be good to fly on 12/11 if all goes well, though I'd play it safe and not book them before 12/12.)
Also note that on DEFRA's site it specifically says
6 calendar months, so you can't just cheat a few days off and do 180 days.
I don't think there'll be any fees after next week for a while. I'm sure the USDA vet will charge something to fill out the EC 998 form that's valid for travel for 4mos., and there'll be one more vet visit to pay for to get their flea/tick/tapeworm stuff done right before they fly. That should be it, though.

(Besides, as Stoatula pointed out, the rather insane cost to get them on the plane itself.)
Hope that helps!
PS - in case it matters, this is a "normal" vet (I do all my regular/routine stuff at a low-cost mobile vet) in a suburb of Raleigh, for cost comparison.