I've bought and sold quite a few napkin rings over the years. There are a number of obvious factors that determine how much you can expect to get such as: a collectible silversmith/retailer, the premium that can come with a Chester Hallmark, the weight, how crisp the marks are, damage-free, design, weight, whether it is monogrammed (some initials can enhance the value quite dramatically if you have two bidders with those initials, just think how much it would cost to have the engraving done nowadays) , whether there is a pair and whether or not in original box.
I have made handsome profits, frequently doubling my money on many of them. The ones that have made me the greatest profits have been ones that I've bought at local auctions, cleaned up and sold on ebay ... and also ones that I've picked up for a snip on ebay and then sold on ebay for a nice profit. The ones that I have often targeted in the past have been poorly photographed ones, that haven't been cleaned and and even ones which seem to have a small 'ding' or 'dings' but with no mention in the description. I polished them, took very nice, clear photos, gave full description including reference to any minor imperfections, and generally achieved top dollar. Good photos are very important when selling, poor photos can benefit a speculative buyer .. So take good shots of your napkin rings, including a clear one of the hallmarks. Use a background that complements silver, the brown leather makes them look tarnished and 'thin' ..... Good Luck!
ps
I have always started my listings at £4.99, maybe because I could not bear to have them go for 0.99! But it is still a low enough starting price to keep people interested. I've often seen napkin rings that have a starting price which reflects their scrap value and often they go unsold, or get the one bid.But that is only my opinion, you need to have a starting price that you feel comfortable with.
