The existing pipe goes directly under the tree which is at the curbline. Any sort of digging operation would involve either cutting down the city-owned (and there's no way I'm cutting down this perfectly healthy tree just for my convenience) tree or opening the street. Either of those will certainly cost more than the relining. I suppose that one could tunnel under the sidewalk and tree, but that would require much more than a trench - you'd have to put in some structure to keep the whole mess from collapsing. I can't imagin that would be cheap.
It will be another day or so before my work schedule opens up so that I can get competitive quotes and stop by a couple of plumbing supply places.
[not in response to this post, but relevant nonetheless] I mentioned to my wife that I was getting good responses from this group, and that someone had suggested that it would be a bigger PITA to have the pipe fail on December 23 with a foot of snow on top of it, and she reminded me that about ten years ago, our water heater had a catastrophic (spectacular!) failure on Jan 31, with a nor'easter predicted for that night. It did cost a few extra bucks, but we did get it taken care of before the storm.I saw, painted on a septic tank pump truck, "It smells like money to us!"