Aaahhhh I love Harajuku! I went there a lot when I was in Japan last year, it's an awesome place. I'll know quite a lot about it now so I'll post what I think might be interesting! Sorry if this is info some of you guys know already though haha ^^
I like to think of Harajuku as having 3 main areas
Takeshita street
The famous crowded pedestrian only street which is absolutely chock-a-block with people most of the time especially on Saturday and Sunday. You can find pretty much all kinds of youth alternative fashion and mainstream fashion here and there are girls and guys dressed in all sorts walking up and down. People watching here is so much fun! There's loads of shops with super cute kawaii decora-style stuff, lots of punk and goth fashions, lolita-style stuff, some sexy gyaru fashion, lots of accessories, shoes, lingerie shops as well. Even a couple of clothes shops for dogs! XD And of course lots of fast food places and many crepe stalls where you can get those famous Harajuku crepes stuffed with cream, cheesecake, and whatever you want! ^^ They also have idol goods shops on this street (think Johnny's photos, concert goods and posters etc) and many places to take purikura! And a very big 100yen store where you can get practically ANYTHING (some lipstick, a plant pot, a set of chopsticks, some socks...) for 100yen as the name implies. Awesome x)
Ura-Harajuku (Harajuku back streets) where you find lots of cool, alternative guys' fashion much of which is music orientated, also girls fashion here too, and lots of hair salons etc. This area is pretty quiet compared to the others.
The main streets and crossroads leading to Shibuya and Omote-sando
Has loads of massive department stores (LaForet is one of them, the big store with a lot of alternative fashion (Lolita, Punk etc) on the bottom 2 floors) and lots of foreign brand shops (H&M, Topshop, Forever21...) as well as designer brands etc.
Meiji Shrine and Yoyogi Park area
This is the area with the famous Cosplay/street fashion bridge ^_^ As zucker asked about, and Tsuwabuki mentioned, there's not always a lot of cosplayers nowadays though... it is a little bit of a myth (as in there's not usually so many that people imagine there is). But if you're lucky maybe you'll see quite a few! Best bet is to go on Sunday from about 11am I think. If you are lucky and you go on a day when there are many cosplayers or fashionable people there it's definitely fun and they'll be totally cute ^_^
This area is close to Yoyogi park where people do street performances, and a concert hall which is always flooded with Johnny's fans whenever there's a concert on there ^_^
Oh, and also, yes the prices in Harajuku are generally cheap, at least in the smaller shops! There are often sales or reduced items in shops where you might be able to pick up something for just 1000 yen. And a lot of shops have a general price range of 1000-4000 yen, which is very cheap considering how cute the fashion is. Quality is generally not too bad either. Of course some shops are expensive though especially the more unusual clothing like the Takenoko store or some Lolita or punk shops.
Harajuku for me is basically a place where you can dress how you like and you won't get judged at all. The close minded or traditional people in Japan I'm guessing don't usually don't go there haha. I mean you don't often see a lot of people over the age of 30 (or, looking or acting like they are older) walking around the streets there. It's a place full of youth spirit reflected in the awesome things you can see, do and buy there. Anyone who goes to Tokyo should definitely not miss going!!
EDIT: Some pics if anyone's interested!
My friend is in the pic, at the time I didn't imagine putting them up on forums lol.
