How much do these usually get? 300$?
There was a big injection of SSKs into the market thanks to our resident seller. I've been seeing them go for between $185 and $235 lately.
If these are original IBM APL caps, I'd expect that to add maybe $125-$150 to the sales price. If they are Unicomp's, those sold for $40 a set, IIRC. But a lot of people don't like them, so it's not likely to add to the perceived value over a stock SSK. It might even lower the price if the original caps with sublegends aren't included in the sale.