As already mentioned, you need to design for low consumption - both hardware and software. You also need to MEASURE what it is, under 100uA is generally low enough to make most products viable (and the sort of figure that's aimed at commercially).
Here's a short list of things you MUST do:
1) Switch the power to the RFM69 using a I/O pin, so you can switch power to it only when you need to.
2) Place the processor in sleep mode when not transmitting.
3) Use a low power 32KHz oscillator as the sleep clock, PIC's have this capability build in - presumably an AVR does as well? PIC's use TMR1 for sleep, and you normally set it to generate an interrupt every second, and use that to run an RTCC which also sets the trigger for the next transmission. There doesn't appear to be any such crystal on the Pro Mini, so you might need to choose something else?.
4) Make sure nothing is using power that doesn't need to - such as the LED on the Pro Mini - remove it.
5) There's a link on the Pro Mini board to bypass the regulator for low power applications, the datasheet of the existing regulator doesn't tell you how much it wastes - you might be better using an external regulator, and bypassing that one. The ones I'm using only use 16uA quiescent current.
If it's any help, I'm looking for 5+ years battery life, and probably transmitting once a day - using a PIC, with no special precautions (no sleep), and transmitting every 5 minutes (for crude battery life testing) I got over 5000 transmissions, and this is via a GPRS modem. As the PIC wasn't going to sleep, that wasted 6.5Ah battery life - more than your AA's could even provide.
So it's vitally important to use sleep, and you'll probably need to change your processor to something more sleep friendly?.