Simplest Light triggered relay
simulate this circuit &ndash; Schematic created using CircuitLab

If you used TO-220 MOSFETs to switch the relays, you could drive them with photodarlingtons such as the OP535A (to shunt away gate current). 

You can experiment with the value of R1 to get the desired sensitivity. Try maybe 10K to start. At four components per relay driver, I don't think you'll get much simpler.