You're looking at it wrong. You're not paying $10 for 3 or 4 springs. You're paying $10 for a couple hundred springs. The first link, they even come sorted in a nice little case. If you do this sort of thing often, it's nice to have an assortment of crap on hand. One day you'll go, "AH! I have that!" That's how I've been going about it. Now the cabinets above my work bench are stocked with crap.
Take cotter pins, for example. About a year ago I needed one or two cotter pins. I could have gone down to the local hardware store and bought them for less than $1. Instead, I bought an assorted case (just like those springs) of cotter pins. I've used several cotter pins since I bought them. If I needed springs, I would probably by a set like that one I linked.
That, and I don't think you're gonna be able to buy just 4 springs from some where on the internet. Even if you could, you'll end up paying like $5 for shipping on top. That's just what it is. Another example, I currently need to find a replacement plastic book spine. I've only been able to find lots of 100 so far for $10. What am I gonna do with 99 plastic book spines?
You could go down to a local hardware store and try your luck. I'd imagine a good hardware store would have an assortment of springs, much like how they have nuts, bolts, washers, etc. And you'll probably be able to buy them by the spring, at like 10 cents a piece.
PS: If anyone can help me out with finding a replacement plastic book spine...
edit: A homebrew solution might be to use rubber bands. It would probably take some effort to get them the right size/tension, but I don't see why rubber bands couldn't replace springs (aside from the fact that they dry out and break).
