Is Coinbase my only option?
I would suggest trying to become a liquidity provider on localbitcoins.com. You can generally buy bitcoin at below market cost, however you will need to wait for people to take up your offer and would not be able to buy exactly when you want.
Sounds very interesting! can you explain more in newbie terms?
What you would basically do is setup an offer to buy bitcoin on LBC at something below the market price (it is priced in percentage terms of the bitstamp rate, so you could set it to 90% of the bitstamp rate). Then you would need to wait for someone to accept your offer, fund escrow, then you would send the other person payment as per the terms of your advertisement (You would say how you plan on paying the seller - you could choose to send them a western union payment for example).