What have you found to be the most economical and productive
material for starting tomato seeds, and others?

I've used Fertilome potting soil for a few years and had great success,
this year I tried "Master Gardener" (or something like that) organic stuff,
made from peat moss, vermiculite, composted chicken manure, composted bat
guano, worm castings, and various other goodies. My seedlings have only
been up for a couple of weeks, but so far, it's done at least as well as the
Fertilome.

It's certainly not as cheap as using your own compost or anything like
that, but it's not all that expensive, either.

steve