We have a handy person who would do the install
and I would not want to create problems for him
in bringing in a used unit.

I would place a "wanted ad" on craigslist and be very specific as far as what size you need...

Measure across the opening. That'll be the size of the unit.
Most are 30" if I recall correctly. the depth is a standard to fit most counter tops

Can't see how a used unit will save on much Run of the mill stoves are pretty cheap.

The middle market stoves such as Kitchen Aide for $5-Gees are far worse than the old school Caloric brand that Grammy had.
With stoves, either go top of the line or not. The mid range units all suck.
They try to incorporate all manner of stupid crap like glass tops that shatter, computers that are poorly shielded from humidity and lock up, and convection fans that fall off their shafts. Those were the issues I had with my $5,000 Kitchen Aide.

Had a Kitchen Aide Fridge too - - Total suck job~!! The poly interior shell cracked in several places, the knobs fell off everything, Drawers broke, the thing rusted, it refused to keep even temperatures . It was awful

I have a kitchen Aide Food processor that is 30 years old and will not die. I keep trying to kill it 'cause I want a Cuisine Art - Don't ask me why I think I just like the look. My daughter has their big dog stand mixer and she loves it and it too is bullet proof but, their appliances are quite possibly the worst on the planet.

Size is the important thing, so you will need to buy something to the same size.

As to changing to gas, that will involve fitting a gas pipe into the stove position.

Gas cooktops are great, but I loathe gas ovens, especially in australian summers. YMMV.