Thanks. It's too bad that coinbase's price is about $13 higher than campbx :\
At current prices, $13 is about 6%.
Historically Bitcoin increases in price at a little over 6% per week on average, so buying from Coinbase instead of CampBX means you're buying at next week's prices instead of today's prices.
However you can't actually buy at today's prices from CampBX, because now the only way to get dollars into the exchange is to mail a personal check or money order.
How long does it take from the time you mail the check/MO until it becomes available in your trading account?
Approximately a week (depending on what day of the week you start from).
Funny how that works out, isn't it?
Remember that Coinbase locks in the exchange rate when you initiate the order, but with CampBX you can't do that until the funds clear.
tl;dr: If the price is trending generally up, just buy from Coinbase and don't worry about the spread because it's going to be a wash anyway. If the price is trending generally down, mail a money order to CampBX so that you buy at a lower future price instead of today's higher price.