Are you sure? Looking at my Soulver macOS receipt I did purchase it for $10 in 2012. I can't tell if it was a sale price but would be coincidental to have the same price cut 7-years apart.
And, the single-user license I have from June 20, 2010, was for... $24.95!
Maybe it was on sale when you bought it, or maybe the price dropped substantially after I bought it.