The 24 and 32 gauges are obsolete and haven't been sold by anyone for 50 years or more. If you can find one, you may well pay less than $200 for it (if you don't show too much interest in it). It won't be new, of course, but it may well have seen little use.
Look in Shotgun News.
when was the carolina arms 16 gauge single barrel shotgun made
1901 single barrel shotgun, washingtion
It isn't.
How much is a 16 gage single barrel shotgun model 350A Revelation
An early model Lefever single-barrel 12-gauge shotgun with a 30-inch plain barrel can be found for sale online for $300. This is the price for one that is in excellent condition.
50-75
Numerous companies in many countries have made single shot 12 gauge shotguns.
$75
$50-$75
Store brand from turn of the century
50-100 USD
50-100 USD