I've been slowly picking up all of the components one would need to change my Trek 7500 hybrid Deore drivetrain into a Shimano 105 setup. I have caliper brakes, STI shifters, a double crank, front and rear derailleurs, cassette, a rigid fork to replace the crappy suspension system, and a new bike seat to replace the stock one I've been riding for the past year and a half. The only remaining items that I need, which I will probably buy new are the chain, bottom bracket, and the drop bar.

Does anyone have a rough estimate what a LBS would normally charge (minus the new parts I will be buying from them) to switch out a drivetrain? I would try to do this all myself, but I'm fearful of running brake wiring, cutting the fork, and changing the crank.

Soon this bike will be my ultimate commuter and weekend rider!

I wouldn't be surprised if it ran in the neighborhood of $80, maybe more. You've got a crown race removal and install, BB removal/install, brake/shifter install, handlebar wrap, etc. It could easily take a couple of hours.

Buy the remaining items.

Put on the new seat. (start with something easy to build confidence)

Tear down the rest of the rig, minus any headset work.
Install the new bottom bracket and affix the crank. Very simple.
Attach the new derailleurs.
Attach the new brakes.
Attach the STI levers to the bars approximately where you want them.

Bring your partially assembled bike to the LBS and have them finish out the front end assembly and cabling.

Hmm, that is a good idea. I can definitely attach the brakes and try to change the crank. I'll have to see if I have the right sized tool to unscrew it.

Speaking of wiring brakes, how hard is it to do that?

The actual wiring should be fairly easy. Just make sure to keep your old housing so you can cut the new housing to the same length. Adjustment of the brakes may be a bit difficult as you'll want to have something/someone hold the pads close to the wheel while you tension the line. But, as pointed out before, you can do all the cabling and just have the bike shop tune it for you.

Yep. If you're not comfortable with toeing in the pads and all the fiddly adjustments, then just run the new cable.

Don't try to cut cable housings yourself unless you have a crimpless cutter. The inner coil of the housing will get out of round and bind up your cable. Use the old housings/ferrules if they're not grimey and corroded, or have the shop cut new lengths for you. Same goes for shifter cables.