Buy a Hornady LNL and take the bullet rebate
I often use my LNL AP as a single stage.
I can't speak for other manuf's ease of use in this context as I have no direct experience.
What I
can say, is that it would be impossible for it to be any easier than it is on the LNL press.
Shells are held in the shellplate by a simple spring- you simply take a case out, put it back in just as easily.
When doing load workup, or precision loads where I need to make sure I'm spot on with the powder, I just load a single case into the shellplate. Decap/size at the first station, seat the primer at the second.
Pop the case out, weigh it- then back into the shellholder.
Drop the charge, take out the case, weigh it to verify the charge.
If it's right, back into that station and advance to the bullet seater.
If not, empty the case back into the powder dispenser, and drop the charge again.
The LNL dispenser is almost always within a tenth even with extruded powders.
If you really intend on using a progessive press as a single stage a lot- the LNL definitely deserves to be considered as part of your due diligence.