For my current project, I need 5VDC rail to power an ATtiny85, an RF module, and an Ultra-sonic range sensor, all of which require 5V. 5V ensure that the ATtiny85 can be operated without crystal at the desired clock frequency reliably, and it also ensures sufficient range for the RF module etc. The total current draw expected, is about 50mA on average, and about 80mA peak.
Currently, I am considering powering the project using 4 AA (alkaline) batteries, in series to get a peak voltage of 6V. Keeping the project low-cost, in low volumes (say, 10 odd pcs), is one of the objectives. Would prefer to keep the batteries until their terminal voltage runs down to about 1.1V, i.e. for series connection, about 4.4V. Are buck-boost switching regulators the only option ?
Edit: Reading around (arduino.cc forums) I found an alternative proposal, which seems to be low-cost and feasible, but would be good to have some community feedback anyway --
Use 3xAA alkaline (4.5V when new but down to 3.3V after run-down), with the DC-DC boost regulator like this one, selling for a what seems like a rather good price (within my project's budget). It can boost the inputs voltage between 1-5VDC, to 5VDC, supplying max current of 500mA (way more than sufficient for my needs). If this works, the only challenge is finding battery holder for 3 AA's. I've only seen those cylindrical, 3xAAA holders, but nothing for 3 AA's.