I gotta back up a minute here. I talked to the dealer today and the grass catcher is more involved than I thought. I thought it was just a chute up to a bag. It actually includes a blower that attaches to the rear PTO. Still pricey since it depends on the tractor to actually power it, but it isn't as wildly out of whack as I thought.
I asked about the mulcher kit and he said it consisted of a baffle inside the deck that changes the air flow to direct the clippings back into the blades, a block off for the exhaust that extends into the deck a bit (not just a blank off plate) and the blades... it runs about $300 for everything. The blades were $66/set by themselves. I'm sure you could get by with less expensive aftermarket mulch blades.
Ian