That's in reference to the desirability, not the availability. When I say "all else being equal" that is in reference to the future version of the same comparison. If one option is cheaper now, it will most likely be cheaper in the future too, and if it is cheaper then that means it is less demanding in terms of resources to acquire, and if it is less demanding in resources it is "easier". You might have a special case where the less expensive option will suddenly become much more difficult than the expensive option to acquire, but there is no reason to assume in any particular instance that's true.

For a more concrete example - if you have bought a $10 and a $100 ticket, buying a second $10 ticket is, all else being equal, preferable to buying a second $100 ticket, regardless of how desirable either option is.