I have a stag handled sgian dubh that I bought in the late 1980s with a very similar etching. It says "J. NOWILL & SONS LTD" "SHEFFIELD Gr. BRITAIN" with "SKEAN-DHU" in the scroll.

I paid more than $13 for it (thinking mid-20s), but a lot less than $450. The eBay example has crisper detailing on the metal throat to the sheath than mine has.