What ever someone is willing to pay is the simple answer.
What they are worth and what they sell for are two different things.
Price doesn't seem to go by rarity, since some people think they are all rare, but there are many versions from different molds. I can tell you the type you have with the hole in the bottom are more rare than solid bottom. Not saying there were fewer made, they just don't come up for sale as much as the solid bottoms. That style last sold on eBay in 2011 and was listed in a batch of old stock Woodman's was selling off. I think they sold for around $150. At the time I was outbid on them, (rarely went over $100 back then, my best set new in box was a Buy it Now for $25 !!) I'm still kicking myself for not going higher on these.
Here are the eBay pictures;
Condition should play a big part of price, but many times very poor condition sells for as much as very good. It makes no sense, I guess due to no book value.
There was a time I would buy most any condition feet for my collection, then upgrade as I found better. Now most of my collection is in new condition, so signs of corrosion or rust on the cast iron such as yours is more for a user than collector. I paid 163.50 plus $8 shipping for a set of like new cast iron, white brass plated a couple years ago. (color changes drastically, they are more gold / brass color in normal light) By today's prices they may be worth easily double;
It depends on how well yours cleans up. I'd try Maas polish for precious metals since it does very well on bare cast iron as well.
The most common angled feet are selling for ridiculous prices, even painted needing replating.
This nickel set in good condition sold for $250 in 2012. That style in that condition should sell for much more than the common angled variety if people realized the rarity and age. So the common ones are overpriced and the rare sometimes go for less. Go figure.