I can tell you, as a someone that used to work for a garage, they are out to make the easiest buck (well, who isn't anyway?)... The easiest buck for them, with the greatest markup potential, is to replace the whole starter. However, if you are into spending the least amount so you can have fun with the rest of your money, always rebuild what you have (on something this small. If it's very big, time is sometimes more important and we buy a junkyard motor or a crate tranny, or what have you)...
So, I'm sorry you had to pay a garage to rip you off... but that's in my eyes... I personally have the ability and resources to take out and rebuild my own starter if I so choose... For you, it was probably money well spent because you got your car back and _may_ not have had the ability or resources to do it yourself.
There may be pleanty of places to get your assistance at... but I'd bet that on a 'trep, this is THE cumulative source for the best information to get it done yourself.
Makes me wonder... what do you (anyone) suppose the collective years of turning a wrench we bring to the board???
I'll start... 2 years on my own stuff as a 'kid', 2 years school, 2 years in a shop, 10 years on my own.
So, by ASE standards, each year of school is allowed to be considered 1 year experience... so that's 15 years... NEXT?