What is the spa load? Assuming it's two-phase and there's a circ pump, heater and jets?
An SSR does not wear out like a contactor or relay, but they make a lot of heat. About 1W per amp in a one-pole SSR. So you need a heatsink and good cooling for two SSR's. A decent manufacturer of SSRs like Crydom is expensive then add on the heatsink costs and a place to put them. Cheapola Fotek SSR's and the knock offs are just a hassle as they fail easily, due to the fake specs and bad thermal design.
The highest cost is switching high current. If you can instead find a way to cause the spa controller to shut off the spa, it would be much easier. Like tapping into the run/stop switch or falsely trip a safety limit switch such as low water. The spa should already have some control logic.