I'm truly amazed ol' Bob hasn't jumped on this one yet ! Teevee, base rock is a good alternative option. But will Tufa not also serve as base rock ? I agree with Jon. It all develops characteristics, both visual and biological, similar to the original live rock from which it was seeded.
Full stocking of live rock is just not a financially viable option for most. Regardless of the time commitment.
The big risk which was mentioned is undesirable "elements" which may be present. I've heard Lava rock can be notorious for that and thus create algae problems but I wouldn't know anything about that...
. If ya' want some lava rock let me know...
Over the years I've gambled on many "cheaper alternatives". Some good, some bad...it might work for one yet be a failure for another. Go with the Tufa rock. If it's bad you'll know eventually...
