I am not sure what they would have cost then. I would guess somewhere around $300-600 on average, but that's a total guess! I found some sites that may be helpful. It seems Chanel is slightly less expensive than Prada (I found one site that says the average Chanel shoes are $100-$300) and yes, Lois would have bought them in a high-end department store. I think a good model for this store is
Bergdorf Goodman on Fifth Ave in NYC -- they are also really famous for their amazing window displays.
Some other sites that may be useful:
Prada shoes Chanel shoes Have fun making our girl stylish!