Hey, I feel for you! I just came outside from fixing my ignition switch.
It locked up on me a few days ago outside of Blockbuster videos. Key would not turn, so I had it towed to a nearby shop, where they said the only option was to drill it out and replace the cylinder, and the expensive part that contains the steering wheel lock, etc. This job would run about $700 at the MB stealer, and the shop where I was wanted about $400(+/-) to do the job.
Quickly, I jumped into a nearby phone booth and changed into the superhero known as Cheap Bastard, who slayed the bill with his miserly habits. Cheap Bastard requested that they drill out the lock, but go no further. After doing this, Cheap Bastard reasoned, the car could be started with a screwdriver until funds could be found to do the job correctly.
I drove away for $95 bucks as Cheap Bastard waved and rode off into the sunset.
Now, I could have stopped there, but instead I ordered a new cylinder and key for about $38, and a new black sleeve thingy (bezel?) that screws over the lock. I saved the original chrome trim ring.
When I got home today, I found the parts on the doorstep and started the installation process, only to find that the real problem was (and likely is in your car) the dead bolt lock in the expensive part (I forget what it's called). It seems even with a new cylinder installed, the key wouldn't unlock the dead bolt and I had to take it out, moving the dead bolt away with a screw driver (it takes some practice, so be a little patient with yourself).
To keep the dead bolt from causing me any more grief, I wadded up a little bit of paper and shoved it in the gap, holding the deadbolt latch permanently in the open position. I then installed the cylinder. Using a "paper clip in the pinhole" as described in other posts, I held down the little latch on the side of the cylinder while screwing down the black bezel thingy over the keyhole.
So now i have a working key (it dsoesn't match, Cheap Bastard bought the universal one versus paying $95 for a custom ordered matching lock.)
True, my steering wheel no longer locks, but since when has that ever been a theft deterrent in the first place?
For about $150 (including the tow), a few hours of my time and some liberally applied foul language, I took care of this and you can too.

:p
Gil