PoDunkMoFo, You are right, that is not an original stick but close. I think it's a xenophobe stick. Any of the games that used this style 8-way stick from Midway as well as the happ heavy duty can be easily modified to work like the original TRON stick. It's just a matter of swapping the restrictor plate (It's the red rectangular plate pictured on the bottom of the joystick assembly). It looks like this was done on the panel that you linked to or it's an original assembly and just the handles were changed.
As for that panel specifically, I think it's already a little expensive. If you are patient, you can get em quite a bit cheaper than that. It's pretty strange. I saw a nice one on Ebay go for 170$ just the other day but an even nicer one go for just 70$ right after the holidays. I guess it's all in the timing.
If you are not a TRON freak and not 100% concerned about having an exact panel, there are cheaper solutions that should work just fine.
1 - You could do what you planned to do and hack a triggerstick. This would be great for the 8-way phases of the game. All you would need to do then is install a dedicated 4-way in the panel for the light cycles. WAY cheaper than paying big bucks for an original panel.
2 - You could use a HAPP topfire stick instead of hacking a triggerstick. Some folks complain that it's a little awkward to fire with but IMHO, it's all a matter of preference and/or getting used to it. It will still get the job done. Come to think of it, you could make a panel with two topfire sticks, one 8-way and one 4-way or an 8-way with a 4-way restrictor plate. The sticks would cost you around 70$ together but you would have two nice sticks and a panel that is not only well suited for playing TRON but superb for general multi-purpose gameplay as well. Fighters, old 4-way games, etc. and all for less than the cost of an original panel.
3 - wait for that elusive deal on an original stick or panel. They do come around.
Whatever you do, have fun. I'm just discovering this hobby myself and I think it's great.