It's worth a go to try and get the transfer tube loose. I tend to keep the stat housing bolted to the block, undo the b@stard bold and remove the lifting eye, etc.... and slowly work the tube back and forth a little bit using a pair of good, large mole grips, with a thick towel around the tube.
I'd estimate my rate of success of saving the tube, at between 60% / 70%. There is nothing to loose. You can also apply a bit of heat.
Half an hours work can easily save you £50+.
In summary.... if it's a project that's off the road anyway, have a go at separating it. If it's a daily driver which you rely on.... get the replacement tube in advance in case it breaks on removal
Also, don't bother trying to put a new stat in the old housing. The houses vary in flange sizes etc and I once fitted a new stat to an old housing, and it wouldn't open. Created a whole load of work for the sake of saving less than a small round of drinks