It's strictly a matter of opinion. Glock makes a very reliable mid-priced gun. They are hard to beat for the price.
Absolutely!
You'll need to be more specific - there are 5 pistol models that use .40 S&W rounds. They are: -Glock 22 -Glock 23 -Glock 24 -Glock 27 -Glock 35
A Glock 20 (third generation) will retail for about $600 in good condition.
100-400
100-760
For a basic Glock 21, new in box, between $600 - $650.
100-400 or so
100-400 USD
100-400
175-500 USD
400 or so.
300-432 or so