I found that if I used the internet sources for the bulbs the price went down significantly.
I never had to replace my bulb, after I bought a couple of backups (naturally). I would think though that, even though I had my enlarger on a moveable cart, the bulb would be less subject to physical shock then bulbs in slide and movie projectors. And I think that physical shock is a way more important factor than thermal shock when it comes to use in an enlarger.
My Beseler 67 is currently in storage - I switched to an Omega D6 with an Ilford Multigrade head when one came available on local Craigslist. I would prefer, however, to have both installed in a full time darkroom, because there are real advantages to each enlarger.
EDIT: See below for a photo of my Beseler 67 with the colour head "in action" in my bathroom/temporary darkroom. Now just imagine how much larger the Omega D6 is!