While a $5 or $20 Topre is an unrealistic thing to hope for, perhaps it wouldn't be too outrageous to hope for a buckling-spring keyboard like this for around $150:
[ Attachment Invalid Or Does Not Exist ] 17542[/ATTACH]
The default setting would be that Esc, Print Screen, Scroll Lock, and Pause would be left alone, but F1 through F12 would be replaced by 11 multimedia keys - and the one extra key from the 105-key keyboard used for European layouts.
There would be one or more additional buttons added to the keyboard to control how the sixteen keys stretching from Esc to Pause were used. What they were used for would appear in the LCD display stretching above those keys.
Other alternate settings:
Esc/F1-F12/PrtSc,Sc Lk,Pause
Esc/F13-F24/PrtSc,Sc Lk,Pause
Esc/(the ten keys on the left on a 122-key keyboard)(the key in the middle of the cursor cluster)(the numpad Esc, to the left of Num Lock)/PrtSc,Sc Lk,Pause
... allowing normal use of the function keys, and the use of all the extra keys on the 122-key keyboard (so the extra buttons would also allow a shift into 122-key mode)
and the entire Unicode Basic Multilingual Plane, sixteen characters at a time (or 32, since there is a shift key...) - the keyboard would generate the Alt+numpad combinations for Windows, to avoid the need for special software; the extra buttons would be such as to provide "ease" of navigation through such an enormous amount of characters...
and the keyboard would need to be only with a USB interface, in order to have the power to make the display light up.
So, for example, one could have a "<" and a ">" key to choose between multimedia, F1-F12, F13-F24, 122-key, and special character modes - and a separate key that, together with the numpad, chooses which group of special characters is used (and that wouldn't change while you went back to multimedia or F1-F12 modes, for example).
So you could, for example, have accented letters available as:
ð ñòóô õö÷ø ùúûü ýþÿ
à áâãä åæçè éêëì íîï
E FFFF FFFF FFFF PSP
s 1234 5678 9111 rca
c 012 SLu
or mathematical symbols available as:
and so on. It wouldn't take the place of, say, a good Chinese IME, but it would be impressive and convenient.