I've never dealt with Growing Solutions personally, but I say hell no to their brewer price and the "catalyst". If you have good compost and know when the tea is where you want it be (more timing than anything), you don't need a "catalyst".
In your original post, you mentioned the Microbulator from KIS. KIS sells the unit, but the real person behind the Microbulator is Tim Wilson from www.microbeorganics.com
. If this is something your serious about, buy a microscope, microbe ID DVD (I think it's included with a scope) and the Microbulator. Tim used to say the Micro. is ugly but cheap and efficient. If you want the most bang for your buck, then this is the way to go.
As far as sprayers go, it seems to depend on your budget. $2 grand for a 50 gallon setup seems steep. I would look into http://www.gregsonclark.com/products.html
and possibly green pro solutions. Make sure you can spray at least 4 gallons per minute with any rig. I do like your hydro seeder option, but don't know much about it.
For the ride on application, this is somewhat a point of contention, as their is a SS220 unit that some people claim can spray tea. IMO, it doesn't put out enough volume. Look into Z-Spray. They do a lot of custom things on their ride ons and can put together a spray system that would do the job. I did talk to the makers of the T3000 as well. They claimed they had a 50 gallon tank that sat in the hopper as well as a boom and pump that could do the job.