Lately I've been working on how low-power and how cheap I can go for wireless sensor networking on Arduino. Going without a regulator, operating on 2AA batteries, I landed on something that should last 19 months (or on a coin cell for 5 months), for under $12 including battery, and board.
Details here for anyone who might be interested:
Great! Did you try to switch on/off the transciever with a pnp transistor? Or to drive the VCC of the trx directly from a pin (and thus to switch it on/off)?
In a similar design (with bluetooth module) I am using MAX1724EZK33 (~0.8->3.3V) step-up converter with 1.5?A quescent current. Works great when 10uF ceramic caps are used. Mine worked up to 0,5V. You can harvest energy with it and charge the batteries as well 
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Actually, the transceiver has a "power down" mode which uses 900nA, which made it not really worthwhile worrying about it.