Glcok 17 and 19 INFO?

I am going to be attending a police academy later this year. They want us to have either a Glock 17 or 19. I have fired many different weapons before. I am not real familiar with Glocks though. Can someone give me some information on things I should be looking for when I go to get one that fits me? I do have some friends who have Glocks and are going to let me fire theirs before I buy but I want any information I can get. Please no links (my place of work won't let me open weapon related links). I guess what I am looking for is what prices to look for, what to look for if the weapon is used, what type of ammo to use, etc. Any help would be greatly appreciated! Remember, I am not new to firing weapons so I'm not an idiot I'm just not familiar with Glocks.