If you're looking for something like those relays on eBay but want something pretty rock solid, I can recommend these: http://www.digital-loggers.com/din.html
I'll caution you on the link... they made the bad choice to have a video auto-play on it. I know that aggravates me, but their product is great.
I have two of these that I initially used with the network module to control my sprinklers as well as pool/spa pump, heater and valves. I went that way after reading all the complaints about the insteon devices only lasting a season and being very heat sensitive. Though this module isn't cheap, it seems built like a tank.
You can power the device off of just about anything and run each individual relay however you want. I happen to be running all of mine off 24VAC, so a lot of bridging where a power relay could have saved me some connections.
I'll be the first to admit that I probably overcomplicated how I did this, but I had a lot of fun doing it. I'm sure I'm not the only here guilty of that.
The one on the left runs two pool valves (in and out mixing the pool and spa), controls three speeds on the pool pump (off, low and high) and can turn the pool heater on and off by triggering a remote 24/110 relay to kick it on. They're all powered by the 24vac I'm pulling off the AC at the bottom - just a normal Hunter sprinkler power supply. The units draw next to nothing and don't have many relays closed at once anyway.
The one on the right is all sprinklers. It's basically a straight drop-in replacement for the Rainbird that was outside. The distribution block in the middle right basically runs out to where the old sprinkler timer was; there is another block there and that wires in place of it. It's plugged into my local network with a local network address. My ISY can talk to it with the network module and Home Assistant can do the same.
Since combining my ISY with Home Assistant, I've taken most of the day to day control off of the ISY and put it on HA. I like the web interface and I contributed a platform module for HA that makes that brand of relays just show up in HA like normal switches. It makes it easy to make scenes and scripts - not that it's all that hard on ISY. Just that it's never been very Mac friendly. I'm thinking I'll be one of those liking the 5.x when it's less experimental. The ISY is great control, but not what I'm looking for in interface.