Why don’t magic items seem to match their prices?

As an example, a ring of Animal Friendship costs 10,800 gp, while right below it the ring of Blinking costs 27,000 gp, and yet while theyre nearly identical as far as function, they don’t scale the same.

If I were following the rules for creating magic items, I’m assuming I’d get a cost of spell level x caster level x 1800 (for command activation). Yet those variables don’t seem to give me the costs that the SRD/DMG tell me. Animal Friendship costs too much while Blinking costs less than it should.

Yet a ring of Meld into Stone costs 27,000 gp and it does match the formula I’m using and functioning just like the other two rings.

What’s going on here? Is there an error in the costs of several items or am I not getting something?