Well...you may hear some people (NOT ME) say that painting is easy and why should you pay someone that much to do it. (The guy who bid $400 probably thinks that's all he can get, for this reason) HOWEVER, :D (you knew it was coming didn't ya?) think a little more in depth.
For $3950 you get:
* A pressure washer that YOU don't have to rent or buy and set-up...
* Scaffolding that YOU don't have to rent and set-up...
* Scaffolding that YOU don't have to climb up on while using said pressure washer/paint sprayer/etc...
* A mess that YOU don't have to clean up...
* Probably a good days worth of taping and masking every door, every window, every light fixture, every...thing that you don't want to be a certain color. (and stripping off said tape and masking)...
* Another day scraping, caulking (and for that matter just finding) all the cracks that need caulk...
* A professional paint job, fully equipped with all the little details that may take you 5 or 6 mess ups to get right, the same little details that make a good paint job into a great paint job...
* Complete tear down of scaffolding, pressure washer and haul it all away.
I'd take that deal...but then again I hate to paint...in fact the only thing worse than painting is prepping to paint

. (Needless to say, I'm not a painter)