I don't know about Featherweights---but I do have the original receipt from my 1899 Singer model 27 treadle. It was my husband's aunt's mothers. The receipt was for $50.00 paid cash on December 19, 1899. What I can figure out by looking at cost of living info, it would cost close to $1100.00 on todays dollar, but this was also dated 2005 info--and I am sure because of the recession and such---it could even be higher.
Sibyl