Both a triac and transistor can be used to turn things on and off however they are quite different. A triac can control the flow of AC current - a single transistor cannot based on my limited understanding. You would have to redesign that portion of the circuit to use multiple transistors.
what is the part# and cost of the triac you were planing to use?
although it might be possible to redesign circuit for different type
of output, I'm not sure that would create any saving. in fact i believe
it will be only more expencive.