what to do with dodgy battery compartments/holders

[wax+wire]

finding toys at trash n treasure/op shops often means the battery compartment/holder is dodgy.  The terminals are corroded, or fragile and snap.

Just wondering if people have tips of how they solve this.  I tried to move terminals from one machine to another, but for some reason it is a poor connection.

I thought I could buy a battery holder, and put that outside/inside the toy.  thoughts?

A better option might be to make it run of DC power. If i do this, the toy is 3V [2xAA], but I run everything else at 9V [one DC power supply and a daisy chain]. 
What is the best [cheapest/easiest/smallest] method to drop the voltage from 9V to 3V for a toy?

[Circuitbenders]

3.3v is a standard voltage for some microcontrollers, so there should be plenty of cheap power supplies out there.

One of these for a start http://www.ebay.co.uk/itm/261801229379

5 for £3.26 including shipping from china............ how the hell can they do that?