Sorry for your loss.
I would call a few local gun dealers and tell them what you are looking for, i bet folks who own guns pass away all the time and this should not be the first time anyone asked. value will change on model, age and condition. (just like a GMT!
)
get one or two estimates, even three.
offer to pay for the estimate, and take that cost out of the estate. legit expense, and worth it for family peace. I would feel better with an estimate from a person who did not immediately make an offer to buy.
other possibility is to
call an insurance person for a lead to a qualified person to provide a value estimate.
it might be tempting to do a DIY, but in the long term you would sleep better with a good estimate from someone who has experience and knows the state of the market.
remember free advice is worth what you pay for it. (in some cases)