Copper is copper but not all copper PIPE is the same...there are different thickness that can be had a different prices.
I just built my CFC and bought 50ft of 3/8" of refrigeration grade (thin walled-type M I think its called) copper....I only used 25ft of it and bought it for 45 bucks or so shipped.
The problem I found is that HD and Lowes only had 20ft sections of the thicker copper stuff (type L). It was more expensive (48 bucks for 20ft) and was going to be harder to bend since it is thicker stuff. I also read of problems with bending and rebending of thicker copper pipe which is why I went with the thinner stuff.
Depending on how much your HD employee discount knocks off, you might want to consider going online to buy the copper.
I'll also sell you my remaining 20ft (I knocked off an extra 5ft for a pickup tube that didn't work) if you want to make a 20ft chiller...let me know....I'll sell it for what I paid for it plus shipping...just a thought.