why so different?
auto parts warehouse = $20 -$30
O Reily = $10 - $23
rock auto = $13 - $20
topbrakes = $63- $110
advanced auto = $17 - $25

and do I need to replace the shims? one has a crack in it.
what do disc brake shims so anyway?
can I make my own?
from sheet metal?

 

Shims are designed to reduce chatter noise and heat build up. As for pricing, you generally get what you paid for.

 

A good set of pads will have shims included. Don't go for the cheapest, but you don't have to go all out if you don't want to. If you don't autox or drive it like you stole it you should be fine with the better pads as in good-better-best. The lowest price/quality pads have a tendency to make lots of dust and noise. They still stop but have some drawbacks.

 

When replacing the shims, clean them well and use a shim adhesive. If you want to spend the time, I see no problem making your own using the same gauge sheetmetal.

 

i think the differences in prices depends on what they pay from their own supplier + their markup for their own profit. some have more of a mark up than others. and in my experience the cheaper pads offered work just fine for a normal driven street car, and no problems with noise.