Controlling High Voltage device with Arduino
I would recommend sticking with SSRs. You can get them for somewhat cheap from ebay or allelectronics.com. 

But, if you want to use TRIACs, you can obviously do that as well. You will want to use an optoisolator to separate the high and low voltages. I found this (http://www.epanorama.net/circuits/semiconductor_relays.html) to be a very useful resource on how to use TRIACs as a relay/switch.