Thank you all for those considered answers. I have been exchanging emails with David Kreige of Obession (and The Dob Book fame), re his 20" f5 Classic and the 22" Ultra Compact (which would only need a short one step stool for me). I have also considered making it myself, well not the mirror, but using David's book or getting one of Dennis Steele's kits. Dennis offered to just sell me the rings to keep the shipping cost down and I could source the rest locally. SDM is way out of my league I think but they are great examples of fine furniture as telescopes, I'd be worried about damaging the finish. I love the 25" folded dob he built, the first one I have seen and it eliminates the need for a ladder but I am sure the cost is way out there on that one. I assume it's a RC type design from the look of the front obstruction baffle.
http://sdmtelescopes.com.au/scope-sh...ded-newtonian/
Re the budget for buildings, observatories etc, my garage/shed will have to do, and there will be a space restriction there as well. I am pretty sure I can get a 20 or 22 in there easily but anything bigger is going to require throwing stuff out (not a bad thing in itself). Allan_L is right about the ladder and it's likely that anything that requires more than two steps on a short step ladder or stool is out of the question. Moving the scope to a dark site is also going to be a constraining factor. Right now I use ramps for the 16 to load it but anything larger, even if compact like the 22" UC is going to be heavier in component parts and maybe require a winch up a ramp or a dedicated trailer (and I can't tow my camper trailer at the same time). I guess I could buy a van and carry the scope in that, a fair number of people seem to have them in vans. I am getting the impression that using and living with a big Dob requires some compromises in other aspects of our lives, sort of like having a very large dog, or a horse.
BTW David Kreige mentioned that he is going to be in Australia in April for the event at Coonabarrabran (Sidings Springs), so that might be a good chance to talk to him in person.