Well, if you already have a bunch of 7812s and 7805s, and heat sinks for them, and you are not concerned with burning off about 12W of power, why not use them. You'll probably need a good heatsink for the 7812. Run the circuit for a minute, if the 7812 gets too hot to touch, you are overloading it. There are also ways to use these regulators as the "brains" for higher current pass regulators - see the application notes on the data sheets.
Otherwise, DC to DC modules are cheap and widely available, and can cost only a little bit more than two 7800's and all the heat sinkage you need for the linear power regulation. They are much more efficient if you are running off batteries.
I'm intrigued with having 30V DC as the available power source - rather exotic.
I have found lots of 48V-secondary transformers in the trash. I have a whole bucket of them. Which is odd because 48V DC is a standard telco voltage, and you'll get less than that when rectifying 48 VAC. But, anyway, they are common. So you get about 30VDC from rectifying that.
I bought a handful of these: http://www.seeedstudio.com/depot/Adjustable-DCDC-Power-Converter-125V-35V3A-p-1534.html?cPath=1. Although I would take the 3A claim on the one above with a grain of salt given the size of the heat sink. It is good for at least 1A without getting noticeably warm.
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