Before I moved, there was a specialty store that sold Dutch Process cocoa for $8.50/lb. If I had realized what a good deal that was, I would have stocked up with 10+ pounds! It's killing me that the cheapest I can find it is $14/lb (I've only been looking on amazon). There was one other product that was cheaper, but with shipping, it was more. Is that the cheapest I'm going to find? Is there somewhere else I can find it cheaper? I'm fine buying a few pounds at a time to save money.
If you don't require pure dutch process I recommend Special Dark, it's a blend of dutch and regular, and it works very well in recipes. With S&S it's $6.40/pound.
Before Special Dark we used to use dutch cocoa from AmericanSpice.com, it's $8/pound in bulk plus shipping.
Penzey's, which is excelllent quality, has it for $11.30 lb. and they're currently offering free shipping on orders of $30 or more.
Different DPCP's have different tastes. It will affect the final quality of the cake. I would suggest trying brands first. We have a very cheap fair trade DPCP locally, but I wouldn't change. Guittard is so different.