Yes
A Glock 20 (third generation) will retail for about $600 in good condition.
$300-$500, depending on condition.
No.
Brand New Glock 19 (generation 3) approx R8200 (VAT Included) from Dave Sheer Guns in Johannesburg.
Glock 17, Glock 18, Glock 19, Glock 26, Glock 34, and, if you count the 9x17/.380 ACP in this running, the Glock 25 and Glock 28.
Depending on the model generation, a 80%+ G17 is worth between 375-450$ on average.
A new Glock 22 typically runs about $500. A used Glock 22 in excellent shape can range from $350 to $600. Everything really depends on the generation it is, condition (which should be perfectly fine, i mean it is a glock), if it has any extras, and if it is police issue or not. I would say a police issue in good shape would probably be worth $500-$600 easy.
The company that manufactures the Glock 35 is Glock. The Glock company has been producing glocks since 1982. The creator of the Glock is Gaton Glock.
No, they are different calibers. A Glock 17 is 9mm and a Glock 23 is .40 S&W. A Glock 22 magazine would fit in a Glock 23.
.40 and 9mm Gen 4 Glocks have been available for several months already...
Glock is a brand