What are the differences between adjustable and fixed Glock sights?   Does one really need adjustables, or are fixed sights ok?

Also, price check on Glock 19 and Glock 26 please.

For a defense gun? Get some good night sights even in daytime trijicon and meprolights give a better sight picture than stock sights.

Fixed sights are my preference.

As far as price, check http://glocktalk.com

Glock Talk is out of commission and has been for at least half a week - anyone know what happened to it?

Everything I've ever heard about the adjustable sights from Glock is that they are fragile.  I've only ever had one pistol with adj. sights (a Taurus PT101) and they broke twice before I finally fixked it myself using larger pin and screw.

Unless this gun is only for target shooting I would avoid them, and even if it were only for target shooting I'd think twice about it.

Get fixed night sights. I was like you at one time and thought 'what if it doesn't shoot where I aim?'. Fixed sights work great. Did have adjstable night sights (MMC I think) on one of my Glocks. They were taller than normal sights, would catch on clothing if you were going to conceal, didn't work in most of my holsters, but they were tough.  $0.02

I paid $499 plus tax on a G19C in austin at a gunshow. Plain jane G19 was about $430-$450. Seems a gunshow is a good place to buy a glock, most dealers have them and they want to best the guy across the aisle. Most dealers were very competitive on price for these guns. Some private sellers were just out of their minds, saw a used G21 w/ 2 postban mags going for $650. P.S. same gun brand new w/ 2 mags is $450-$499. P.S.S. small review on the G19C, excellent gun, jammed mabye twice the first 50 rounds but then loosened up and shoots great now, no FTF's. Not to crazy about the porting, sometimes it will spit crap back towards you, will probably buy a nonported barrel so I can have a choice.

I have adj sights on my G21 and my G17 I like the adj's. Haven't had a single durability problem with either. Realistically you don't really need them. But I like them. I dont like the compensated models the light blast from the compensator is blinding after dark and Yes I do shoot mine after dark. Good sights, and a flashlight on the rail makes a great gun.

All Glocks enter the country with adjustable sights, 'cause this gives them more points on the 'import list'.  Glock then pulls them off and throws them away.  They are generally too fragile for hard use.  You shouldn't need them, you can drift-adjust the fixed rear for windage.

There are two kinds of factory adjustable sights.  The old ones and the new ones.  Both have a square notch outlined with a thick white line.  The old ones can best be described as "POS."  The way to identify them are that the old style actually extend past the rear of the slide (!).  This is their main (but not only) problem.  They can be, and have been, knocked off during CCW or, in my case, while the gun was in a paddle holster in the console of my vehicle.  If you are buying a used or reconditioned GLOCK that has these, factor in the cost of relacement.  
The new style are not bad.  I have not had to adjust them, every GLOCK I have bought came ready from the factory to shoot 155 gr .40 to point of aim, both fixed and adjustable.
Most people eventually upgrade to night sights.  You can get 3 dot night sights from the factory, either mepro or Trijicons.  I think the Trijicons run a little more.  The most poular aftermarkey night sight seems to be the Heini "Straight Eight."  I prefer the AO pro express, with a big dot for my G27 and G23 (trnslate for your purposes G26 and G19) and the regular dot for G22 and G35.  There are a lot of people who will steer you away from these sights.  
Anyway, good luck.          

Dont really need sights on Glock 17, just point and shoot.(18 times)[pistol]