Checked out local Dollar Stores (and a few other places) for plausible found objects I could use. As I am currently constructing it, there are sort of four classes of approach, more-or-less from easy to hard.
1) NERF repaints and existing model/resin kits. Only the latter has potential; the look we are after doesn't match much in the way of modern toys or props. I have a resin "Dex" gun from Sky Captain but it isn't a great pull -- cleaning it up to my standards is roughly equivalent labor to making my own from scratch. I may drop it in a paint bucket during this project just so I have something.
2) Found objects. Doesn't currently look plausible. Trouble is, you don't get platonic solids these days in consumer objects, whether hardware or household goods or plastic packaging. Everything is designed, with lots of little details. Details that are too obviously from the design sensibilities of this era. On the surface it sounds easy to glue a football onto the grips of a water pistol, but in practice there's way too much modification necessary to allow those parts to fit smoothly and look right when done.
Found objects works for Steampunk, but even then there is a fine line between a clever re-purposing of existing hardware, and the original hardware being a little too obvious.
This leaves me, for this project, essentially on the next two levels:
3) Traditional modeling. Building up with clay, foam, balsa, MDF, or some of the newer time-saving approaches like shopbot-carved MDF laminates or pepakura base. This can be one-off, or include molding stages to reduce weight and fragility, or be designed around the making of molds. The disadvantage in the latter is that molding material has a certain cost per volume and that puts some pretty firm lower limits on your project budget.
4) Full fabrication. I am making this term up as a catch-all phrase for working generally in industrial materials and with industrial processes; in metals, with milling, also with injection molding, powder coating, and other techniques that are not part of the traditional craft set. Obviously there's quite a bit of overlap, from laser-cutting acrylic to brazing brass, with the latter.
The methods and materials imply a greater cost, but for a project like this there is a trade-off; whereas if I traditionally model, I work from concept outwards to realization, focusing on fabrication means letting the materials and methods largely dictate design. So the elements of the final product are chosen because they fit well with selected fabrication techniques, and the final look is defined as much by the materials themselves as by various finishing processes (painting, decals, whatever).
Simultaneous with above, I'm working on general conceptions. One way or another I am going to do massing studies and mock-ups before I move to actual construction. It may or may not entail a stage of CAD modeling; for visualization, for client communication, to work out tolerances and fit-up questions, and potentially to drive various sorts of CNC fabrication.
At some point the two threads will meet in at least one plan that I can stick an estimate to and mail back.
I've only started scribbling design conceptions:
The major difference between the two larger sketches is one is "zeppelin on a pistol grip" and the other is "electric drill" -- aka, the body and grip are one solid object with no strong separation. The pig is the only idea I got from the Dollar Store. I haven't bothered to scribble out any of the stacks-of-rings or stacks-of-donuts or other typical barrel designs, but in my mind the barrel will be from 1/3 to 2/5 of the visual volume of the finished prop.
There are at least two more major forms I haven't been able to scribble out yet. One is what I might generically call the "slab of plywood with a dowel" look. This is also a mono-body, but with a smoothly tapering grip and a swoop to the overall shape that brings in the Cadillac Fin sort of idea.
"Hairdryer" is also a plausible direction, different from the "zeppelin" mostly in that there is no separate barrel but the muzzle opens out of the main body.
And yes, I really want Googie elements in this, boomerangs and cheese holes and all.
The other scribbles on that example above are just too modern and utilitarian and do not represent useful directions for this project (as much as I tried to work in Barbarella and Moonraker laser pistol elements into them.)
From even these, however, it appears obvious that however much I construct barrel elements from simple cylinders or lathed objects, the grip at least needs to be shaped more, and the body is an open question. So the likely plan is going to involve several different construction methods for the different elements.