You should be able to find or build a 12V-5V switching regulator for much less than $15.
1) Check thrift stores for car phone chargers. A lot of these are 12V to (approximately) 5V switching regulators. Or you might find a 12V to 8V regulator which would power the input to a 5V linear regulator for a nice overall efficiency boost. Most of these are based on the mc34063 switchmode chip, which is less than $1 (for just the chip.) So you can consider building your own. (or import modules from china: http://www.sureelectronics.net/goods.php?id=365
2) Consider discreet circuits like "The Black Regulator" http://www.romanblack.com/smps/smps.htm
Somewhere I have a freeduino board design with a Black Regulator replacing the linear, but I've never built or tested it (nor even a plain Black Regulator), so it's "not ready for prime time." It does fit, more or less.
60% is really poor for a switchmode converter, BTW. Most are 80% plus...
But the efficiency difference IS pretty dramatic. Back in the good old days, large computers had these HUGH linear power supplies. One mainframe I was familiar with, during its decline into dotage, had someone do a mod where "modern switching power supplies" were added to replace the linear monsters. The supplies were small enough to fit in the chassis without removing the old supplies, and the increased efficiency allowed the mod to pay for itself VERY quickly, once you took into account both less power into the computer AND less power used by the air conditioning...