I've seen those type machines around here occasionally, but most of the trees are like the ones in the video. You had mentioned trees up to 48" diameter, as i recall most of these stumpers (feller bunchers) limit out at around 24" diameter trees. For the bigger trees it's time for the chainsaw and wedges.
As far as the cost of dozers, you could probably pick up an older D6, 7 or 8 from the 1950's era for far less than 100K, more like in the 6-10K range. Then this leads back to the question of mechanical skills. These old machine require quiet a bit of work just to keep 'em going as i stated in another post. For some of us, it's almost a matter of love keeping 'em going and sort of preserving the past at the same time.
Newer machines are easier to run, but they have the same maintenance requirements as the older machines. I guess the ultimate question would be the depth of your pockets as to a newer machine versus an older one.