That said, strongly consider anything you can do which pushes your average transaction value up above ~$20 or so. This is partly due to decreasing the bite of transaction fees but mostly because building a business on $1.50 transactions is really, really, really, really hard when Steve Jobs has not already arranged a captive audience with credit cards on file.
One of the traditional solutions in e.g. social games is selling a virtual currency in $10, $20, $50, etc increments and then using the virtual currency to effect small-value payments. For example, $10 gets you 7 dragon eggs, $20 gets you 15 (one bonus egg!) The thing you were thinking of selling for $1.50 now costs 1 dragon egg. This both helps you get your average purchase up, saves your processing costs, and also increases transaction volume by not having people feel like they're being asked for $1.50 on a frequent basis. (The fact that $10 doesn't divide evenly by 7 is not accidental.)