Are you thinking of starting a project to make some? I have a NOS Satan's Hollow stick I could be persuaded to lend out if it were a viable project.
I'd like to, it would be an interesting project to do. Except I have serious doubts I could do it any cheaper than what that guy is selling them for on eBay.
Until someone can make new or locate the original metal injection molds for this stick and set up a small run plastic injection business, this is a situation we're always going be in. 
The answer to your questions are that the Satan's Hollow and Tron sticks are more or less 100% identical... The trigger on the happ stick is also the same but they have made internal mods to the stick design to take modern switches. Externally they are the same stick. The answer here is that Happ own the original molds that were used. So there is not a cat in hells chance of ever getting access to them.
It would require new tooling to injection mold sticks at a cost exceeding about $3000 USD for the mold alone. So the cost is not justifiable in the sales to recover it. But if you could find a market for 3000 sticks, then the price would come down.
The resins involved in making these as a one off item are where the cost comes in, and the equipment. You can't just pour these resins. They have to be de-gassed under vacuum while in the mold and take over 24 Hours to cure. so you can only mold one a day in the mold! slow and expensive.
The other problem is that until they cure these particular resins are extremely toxic. Skin contact for any period can cause illness and even death. Once they cure they become inert.
These are the problems that I was kind of hit with while working on it. There is a solution but it wouldn't produce them for much less than those on e-bay. They are just, well, expensive to make and until I get the rest of my time sorted out I don't have time to further develop a solution.
Best Regards,
Julian (Fozzy The Bear)