Corsets were not expensive in the period 1894-1910 (I have catalogues from that period).
The following from Sears, Roebuck (mail order) for 1908:

"Made of good quality contil, well boned throughout,......." $0.47.

A full bodied corset, the most expensive costs 95 cents. "...Very popular long hip medium high bust..." "made of best quality French contil..." "....fitted with the best non-rusting stays and aluminum eyelets" "...Four hose supporters of the best lisle elastic..." "...finished with valenciennes lace and satin ribbon..."
"Postage extra (if not bought in store) 17 to 21 cents."

A hip corset is offered for 57 cents. A "summer" corset with sateen covered stays is 44 cents.
Similar prices in a 1894 catalogue from a Canadian company.

True whalebone stays were expensive, but largely supplanted with steel in the 1880s. The average person used the steel or did without. A girl on the street would have used the steel 'bones'.