The value of a Topper model 158 12 gauge would depend on a couple different things. The main thing to consider would be the condition.
100 USD give or take
Made between 1962-1974. Model number changed to 058 in 74.
I would pay $1,000,000 Why would you pay that much?
1971
Get help from a gunsmith
$100 to $110 in excellent shape
About $75, more or less.
Depending on condition, $75-$125.
find a replacement barrel and cut to the length you want
The .410 brings more than the 12ga or 20ga, but still tops out at $100-$125 if in excellent condition. sales@countrygunsmith.net
50-200 USD or so