http://www.shroomery.org/11339/Grain-Spawn... Here are some various faqs and teks on grain spawn techniques, for something on that scale brown rice flour just doesnt work very well in my experience, way too many little jars to handle, too many seperate places for contamination to occur, too slow.
With the amount folks spend on hps lighting and so on, the cost of a good sized pressure cooker is nothing, and its pretty easy to prepare rye grain for jars in bulk. I would go with rye grain over birdseed(I experienced more frequent contamination issues with birdseed and issues with incomplete colonization)- you can order it bulk in 50lb bags or pick it up by the pound at your local natural foods store, by premade jar lids, or make polyfil injection sites on the lids yourself, and make spawn in quart or even half gallon jars. Because you can shake the grains around easily, unlike with the brf/vermiculite, you can get the jars colonizing fast and vigorously.
Most every town or even city of decent size has a horse riding stables somewhere nearby on the outskirts of town- a great source of free horse manure. You can pasteurize this manure, by heating it to 160 or so and holding it there for an hour, (can do this by putting manure in a plastic tub and adding boiling water till you hit the desired temp) and then dump it into big rubbermaid type tubs and mix in 3-4 jars of spawn... keep these tubs at 70-80F, ventilate em a couple times a day, and before you know it you'll have a tub full of mushrooms.
You can reuse the jars, reuse the tubs, after sanitizing them, so there is very little cost beyond your initial outlay, especially if you take spore prints and make your own spore syringes. If manure is unavailable to you you can also use similarly pasteurized straw, mixed with a bit of worm castings, but straw tends to be more likely to get contaminated since it is a less desirable food for the mushrooms.
My buyer for them is out of the game for a while, and I dont really know what I'd do with that many mushrooms again. If I do it again, it'd be summer time probably and then only on an automated system with gigantic trays rather than tons of jars.
