Shimano BR-5800 road rim brake caliper set for $50:
Shimano 105 BR-5800 Caliper Brake Set (the-house.com)
$10 shipping, but first time buyer code DF15NM15 gets you 15% off. Otherwise, Microsoft Edge can find you a 10% off code.
The same brakes on my road bike are due for an overhaul, so I bought a spare set in case I somehow screw that up.