No, it's nothing like shipping a book 2 days late. The OP has actual, recognizable economic losses as a result of Coinbase's delay. The transfer of money via ACH is a separate transaction from the Bitcoin acquisition. After the admitted delay following the Bitcoin acquisition transaction, Coinbase should have either reaffirmed that the OP wanted to purchase the coins at the original price, canceled the transaction, or acquired the coins at the then-market price. (Note, normally when the price increases, Coinbase cancels the transaction.) Consequently, the OP has a solid legal case against Coinbase.

Unfortunately, for the amounts involved its borderline not worth pursuing. It's too large an amount for most small claims courts, and too small an amount to justify the time and cost of civil litigation (unless it settles at the very early stages). Indeed, based on Coinbase's record (refunding purchases if BC prices increase rather than executing the transaction), it's very likely that they are factoring this arbitrage into their business model.