So glad you asked!
My own research follows into why I think under $1000 is a pretty freaking great deal.
A quick Google search yielded this information regarding laser tube replacement in general:
Cost for a typical CO2 laser tube in the 40W to 45W range is from $300 to $400. Since these are proprietary, they probably run more expensive than the tubes shown here. That’s just the part cost. I’d guess these run in the $350 and up range.
Here is an Instructable on how to change a CO2 laser tube. And here is a video showing how to change out a laser tube on a randomly selected Chinese CO2 laser. There are additional Youtube videos showing the process of changing out a laser tube if you do a search, but those are enough to get the general idea.
After the new tube is inserted, the power supply has to be set to extend the tube life. This part is dangerous. (And I suspect Glowforge prefers to not fry their customers.) But if you are interested in seeing what’s involved, I found an Instructable for it here.
After the power levels are adjusted, the laser beam path has to be set by calibrating the mirrors and lenses to get a good beam path. This can take hours if done manually, I’m sure the Glowforge team has developed a jig of some sort to set and test it. But if we were to try it ourselves, there’s a writeup in Github about how to go about it. And there are videos here and here on other lasers.
After the tube is replaced, and calibrated, it needs to be tested, and the machine checked for any other problems. Then cleaned up and packaged back up for shipping.
Shipping costs round trip for something that large will run $200 easily. So we’d likely start out at about $550 total for shipping and parts, before even getting into the actual labor.
It wouldn’t be unrealistic for them to charge a thousand bucks to repair one of these things, based on this (and other earlier) research. I decided long ago that it was worth it unless they start charging over $1500. Then I’ll need to decide whether to become an electrician so I can install and calibrate it myself.
Fortunately I can’t give specifics on it since I haven’t had to replace mine yet. But this appears to be a fairly complex process, the parts don’t just snap in and go, there’s a lot of skill involved in it. Skills that I certainly don’t have.
That $500 quote was an estimate from Dan because a lot of anxious people were pressing for it, before they had even had to do a single replacement. Absolutely no one remembers that it was an estimate when the time actually comes to pony up for a replacement. I’m not going to hold them to that fixed number. I think it’s admirable that they’re trying to hit it, but from a business standpoint, I hope they’re keeping an eye on their actual costs.