Snapchat rejected a $3 billion offer from Facebook (disclosure – I own Facebook and Groupon stock), but now its team needs to figure out a revenue model to justify an even higher valuation.Two most likely revenue models are advertising and digital goods/coupons.Due to the ephemeral nature of a Snapchat message, it’s unlikely advertisers would spend more than the average effective cost per 1,000 impressions of $1.48 on an iPhone to advertise on Snapchat. For the purposes of this article, however, let’s assume that Snapchat were to convince advertisers that a disappearing message is a good way to spend their money.If Snapchat served an ad with