No soup for YOU!
I have been biting my tongue as long as possible, but I have to chime in here...
First of all, like anything else, supply and demand dictate where pricing will go on these gearboxes. In the US market, these were only used for a few years, and while a lot were probably made, it's still somewhat of a narrow selection i.e., years and model. Add to that, these are quite reliable cars, and the quality of material and build quality, especially in the engine have kept a lot on the road. As previously mentioned, most scrap yards, and even some Nissan dealerships no longer keep parts or even records for the parts. When I call my local Nissan dealership, there is only one guy who will look up parts of this vintage, and for that matter, he is the only one to have access to that database. I have heard from many people that their local dealer either does not have access to those records or will just be told there is nothing available for that old of a car. I'm lucky because my contact is only known to me because I have a friend that restores (exclusively) Datsun Roadsters. Otherwise, I'm sure I would have run into the same brick wall many of you have.
As previously mentioned, scrap yards don't have much interest in keeping these older vintage cars around, no doubt because they have very slow turnover for parts. In addition, I also know for a fact that there are people out there who either have friends in or make deals with a salvage employee, who will "make a phone call" when one of these Datsun gearboxes come in. Why do you think it's usually the same guys on ebay who always have one or two to sell?? Most times, if you find a 210 in a yard, even if it just arrived, the gearbox will be gone but little else is missing. You can blame them for the high cost of the gearboxes too.
Add to that that Spridget people aren't the only ones looking for these. There are plenty of guys (maybe even more-so) who restore vintage Datsuns (i.e. 1200), that this gearbox is also sought for an upgrade. Imagine the reverse, that there was some precious component on our cars that was highly sought after by some other camp. If you needed that correct part for your car, you'd not be happy about someone else drying up supply or driving the price up. As an example, there is this sort of animosity between MG 1100/Austin America and Mini collectors because the Mini guys will scavenge the transverse 1275 and full synchro gearboxes for the Mini, and scrap the rest of a good car.
When I first started doing these conversions back in 1999, you could get a gearbox from a yard for $75. Even then, there were "hoarders" that would supply Rivergate or would be referred by Rivergate as "suppliers". Even then, people were doubling or tripling their money on them. I bought several back then for $150, but it was never worth my time to drive all over **** and back to find one and then pull it myself. I was happy to pay the price and get on with it. In the last few years, I too have paid market prices for the gearbox. It's still not worth my time to drive all over the valley for one.
Since then, prices have gradually increased, but it still depended on demand. There are times when an ebay $500 box would not sell, but a month later, you see them sell @ "Buy it Now" for $600 to $800... or more.
The reality is, there are people who actually value their time and are happy to pay market price. Let's face it, how many years are you willing to wait to have what you want, and how many years do you have left to enjoy your ride? Is it really worth it to give up the pleasure of having what you want for a few hundred $$? Do you really think they are going to get cheaper in the future? The only time these will get cheaper is when neither I nor Rivergate make the adapter kits, and nobody wants them anymore. The more you "refuse to play", the sooner that's going to happen. I have many times been asked to consider coming up with an alternative kit for a different, more available gearbox, but there is just not enough demand or support to make this a viable, cost effective alternative. You have no idea what it costs to make and inventory everything that's needed, especially at the quality level I have.
Lastly, those of you who who say I wouldn't pay more than... _$____ for one, I would ask "and how much would you sell the one you paid a couple hundred for?" I know for certain that in most cases, the answer is "as much as possible", as in what ebay prices are.