Money can be exchanged for goods and services. And the selling prices of goods and services are determined, in the broadest sense, by the forces of the marketplace. Material things are worth what people are prepared to pay for them. So things that cost the same, are, in this one abstract way, equivalent.
Just for fun, here are two things I bought on Sunday for which I paid, after taxes and member discounts, almost exactly the same amount of money– right around $20 US. It’s an interesting pair of objects, both of which will probably be with me for a while. Which will give me more reliable service? Which will be more pleasing? Which, in the end, will I feel was the better deal?
(Yes, I have decided to reread The Lord of the Rings, cover to cover, including all appendices and supplements. But when I took my original paperbacks off the shelf, they were too fragile to handle, hence the need for the new edition. The quality of modern reprint paperbacks, particularly the digitally reproduced “type”, is appalling. This volume was modestly priced, looked like it will be at least readable, and the cover is only mildly unattractive. )