As someone else mentioned, the UC Davis prices are just the costs of the tests. Even if your vet was having the tests run at Davis (which is certainly a possibility), unless they’re close enough to drive the sample themselves there is the cost of overnight shipping ($) something that needs to stay cold ($$) and is considered a biological sample ($$$). There is the office time of either a staff member or the vet themselves spent coordinating shipping, making sure it gets dropped off, and filling out the proper paperwork both for the lab and for the shipment. All without factoring in the cost of needles, syringes, etc etc. And the lab frequently charges a specimen disposal fee in addition to the test, as well. And UCD actually has pretty reasonable rates for their tests–there are private labs that are 3x as much. So without knowing whether your vet actually ran the tests through Davis, it can’t be an apples to apples comparison.
Also of note, I’ve had multiple animals treated at UCD and the tests had additional markups to the above, explicitly for handling of samples, supplies etc. The prices on you listed are the referring vet’s cost for the test. Not what is actually charged to clients.
I totally understand the frustration, and I’ve definitely paid some bills that had eyebrow-raising markups. And it’s eye-watering how expensive vet med has become. I wish I had a better answer because the financial strain is real.