What's special about a three hundred dollar keyboard? What does it do that a cheaper one won't?
What's so special about a $70 keyboard as opposed to a $5 bargain-bin one?
A $300 keyboard will do nothing more than a $5 one will. But then you have to question what you're willing to pay for what interests you.
A mechanical keyboard offers a better typing experience with different switches, more reliability, styles, customizability, and quality.
With Topre keyboards, they are typically more expensive because only a few companies make them. I believe only Topre produces Realforce, PFU put out Happy Haking Keyboards, and Cooler Master is putting out a board soon.
The cheapest Topre boards you can buy is the Realforce Type Heaven at $150. It gets you a decent board with standard switches and standard everything. It's cheaply built compared to the rest of the line up. Cooler Master's Novatouch is rumored to start at $200 and it gets you a bit higher quality, and also uses MX-Cherry key caps.
Realforce start out at about $220 and go up. Happy Hacking Keyboards go from there.
So what do they get you?
First off, the build of the board is much better. Realforce and HHKB boards are built like tanks. With Realforce Type Heaven, you're getting a cheaply built board.
Second, the key switches. Topre switches are more expensive to product because of high quality control standards. They have the longest life-time of any switches, and IMO the best feel. When I moved from membrane to mechanical, I felt the difference and moving back feels terrible (although, some vintage membranes are amazing). After I switched to topre switches, I can't go back to MX-Cherry, Alps, Buckling Spring, and others. Topre just feel more refine and smooth. However, they do not have many variants. They have a few different weights between 30g to 55g. There's a regular and silent option (which is a rip-off on HHKB, but not on Realforce. You can mod to make the silent version). Other than that, they all have the same feel. With Realforce Type Heaven, you only get 45g and no other options.
Third, they have variable weighs. Meaning some keyboards--like mine--have a arranged order of different weighted keys. This means the keys in the middle of the board are harder to activate than the ones on the side, so ring-fingers and pinkies don't work harder. And some keys like the ESC key are the hardest to press. This does make a difference as there's less fatigue for your whole hand and less mis-presses. Realforce Type Heaven don't have this at all.
Fourth, PBT keycaps. These key caps are stronger, more resistant to wear, and last longer. It takes a very long time to wear the texture off the top of the keys to make them smooth. For example, I've had a Daskeyboard and after three months I wore all the keycaps smooth because they were using the cheaper ABS caps. With my HHKB, I haven't started to wear the top of the caps after a year. (The only negative here is that HHKB, not Realforce, don't have PBT space bars. Sucks) PBT are far more expensive: A set of ABS caps come in around $20-50. PBT start at $70 and go to $150. Realforce Type Heaven uses ABS.
Fifth, for HHKB the layout is amazing. Backspace/delete is moved down a row--above the enter key--so it's easier to reach (set standard as delete, and you toggle it to backspace). CAPS LOCK is removed, finally, and replaced with CTRL--this makes a ton of difference. There's some keys moved around like ~ to the right to accommodate for the layout. and a FN is added so you can use the arrow-keys (and for Mac users, you can have media keys). Realforce Type Heaven has standard layout--like the other Realforce boards.
I'm a keyboard enthusiast, but I ain't crazy. Trust me on that. There's some people out there that order aluminum bodies ($150), specialized keycaps ($150-200), special order cables ($10-50), a custom leather wrist pads ($50) with a keyboard--most likely a MX-Cherry board, so add $100-150 to it all. I'm not big into customization, but I want a good typing experience. I have the money, my keyboard is my main tool for writing, why not spend money on a good one?