Lot of questions, so I'll try to answer a bunch in no particular order.
A lot of factors go into camera prices. Built quality, feature set, lens quality and rarity all effect the demand, and therefore the price. Which camera you want might depend on what factors you find most important. It seems like you want to do more "studio" type work. Pretty much the top-of-the-line with that regard would be the Leicina Special, Nikon R10, Nizo 6080, and Bauer A512. I personally own a Nikon R10, Nizo 6080, and Bauer A512 (although I just got the Bauer working), and of all of them I'd say the R10 is the most versatile, well built, and with the nicest lens. If I could only have one super 8 camera, it'd probably be that one. The Nizo 6080 is by FAR the quietest, so if you want to be able to record sound, that would be the camera to choose (even if it isn't crystal sync). The Bauer A512 has an external low-light meter and a unique long-exposure timelapse feature that I really dig. (A few other upper-end Bauers have the same feature). I believe the Nizo s800 also has a long-exposure feature as well, although it's more traditional than the Bauer's.
Then there are other cameras like the Canon 310xl. This one is not rare, and can be found pretty inexpensively. It might not be what you're looking for, since it only shoots 18fps and single frame, but it's very compact and has an f/1.0 lens, so you can get some nice super low-light stuff. I also have a Beaulieu 1008xl which is pretty nice, has a decent lens, and has a form factor similar to the Nizo 6080, but isn't as quiet. Still, I wouldn't discount it. I've also got a Chinon Pocket 8, which like the 310xl only shoots 18fps, but it also fits in your pocket and weighs only 450g. There are so many cameras and they all have their purposes, so really it all depends on what kind of shooting you want to be doing.
As for ASA or ISO, those numbers tell you how sensitive the film is to light. Every time the number doubles, the film is twice as fast -- meaning it needs half as much light to get the same exposure. So 100 speed film is half as fast as 200 speed film, 200 is half as fast as 400 speed, 400 is half as fast as 800, etc. The D or T after the number indicates that the film is color balanced for either Daylight or Tungsten light. Tri-x is black and white film, so it is not balanced for either (although you will notice that Kodak recommends you rate it differently if you're in daylight or tungsten. As I understand it, this is to compensate for how the film reacts to blue.)
Manual exposure. This depends on the camera, but most of the higher end cameras, and a lot of the lower end cameras actually have manual exposure. Assuming you know how to use a light meter and your camera is working properly, it is exceedingly consistent. Like, scientifically consistent! Really it's kind of remarkable. Thanks, Kodak!
Tips for Tri-x. Expose properly? The general rule of thumb for getting the most information on your film when shooting negative is to overexpose just a little. For reversal film, it's the opposite. But I wouldn't go overboard underexposing your film since Tri-x doesn't have the latitude that Vision3 has. Generally I just expose as recommended on the box and everything comes out lovely.
Developing yourself is very possible and really fun. Developing Tri-x as a negative is very easy. I do it in D-76, but I've also done Caffenol with great results. The reversal step requires mixing up a special type of bleach, so it's more involved and there are more hazardous chemicals. Keep in mind, if you want to process as a negative, Tri-x comes out contrastier and grainier than if you'd done the reversal step.
Here's a Youtube playlist with some of my films if you're interested. Generally I put what camera, filmstock, and developer I used in the description. (keep in mind these are all scanned on a homemade scanner that I'm constantly trying to improve)
Hope that helps!
Edited by Josh Gladstone, 20 December 2014 - 05:09 AM.