The kind of camera you linked to is one of the modern styled round top 600 series models,
http://camera-wiki.org/wiki/Polaroid_600_(round_top) and you could pick these up for next to nothing, less than 10 or 20 quid.
The difference between the films.
80 series film/cameras: dead an gone for decades, never coming back, cameras are display only, some people hack them into 4x5 cameras though. was used in cameras like this.
Polaroid_Model_95 by
diser55, on Flickr
100 series packfilm/cameras: still made by Fuji as FP-100c (colour) and FP-3000b (B&W), produces a 3x4 inch image. This kind of film is sometimes call peel apart film owing to that you have to let it develop then peel the negative from the print, and is used in cameras that look like this (my own Polaroid 355).
Polaroid 355 by
Morinaka_2010, on Flickr
SX-70 series Integral film/cameras: This is the film people think of when they think Polaroid, produces a square image that is self contained and develops before your eyes. Polaroid stopped making this 4 years ago, there is a company called the impossible project (mentioned already) that make SX-70 type film, the quality is well below the original Polaroid stuff and the image usually fades to nothing after a year, also expensive, think £2 a shot, but some people love it. Used in cameras like this.
Polaroid SX-70 Model 2 by
Morinaka_2010, on Flickr
600 series integral film/cameras: Basically the same as SX-70 but is ISO600 not ISO150, so similar that people even use it in SX-70 cameras with a ND4 filter over the lens. Made by the impossible project, same issues as the SX-70 film. Most people who owned a Polaroid probably had a 600 series as they were cheap and mass produced, people practically give these cameras away as they are basically worthless, hell i've even thrown a couple in the bin before. They did make 600 SLR cameras as well with auto focus and built in flash, that look like this.
Polaroid 690 by
hotograph, on Flickr
But most people probably had one like this.
Polaroid Spirit 600 by
siimvahur, on Flickr
Fuji Instax wide/Mini: Same film but different sizes. The wide stuff produces an image about the same size as the 100 series pack film but it's an integral film so develops before your eyes. This film is way ahead of the impossible project, probably just shy of the old polaroid stuff but 95% there. The problem with these is the cameras that use it, they are UGLY and feel cheap because they are, you can buy these cameras new for about £60, problem is they are about as basic as the original polaroid 600 series cameras, 2 focus zones, 1 shutter speed, 3 apertures (light, normal, dark), built in flash, and a crappy lens. This a "fun" system not a serious camera, but to be fair it's still better than using impossible film, the cameras cripple this film wish there was a model with a decent lens.
This is my Instax 200, the new 210 is the same but in black rather than the blue/gray plastic vomit mine is, takes 4xAA batteries.
Fuji Instax 200 by
Morinaka_2010, on Flickr
Anyway, if you are going for a 600 series model i'd get a newer round top design with auto focus, since you mentioned going for the Poalroid One get the Ultra version as it can focus down to 2 feet which she'll be grateful for when photographing people with it.
