Automatic Transfer Switch


I know it isn't completly related, but in a way it is. I'm looking for a way to switch my power from AC to DC during a power outage for my ham radio. A friend has a relay that does this, which was used in an industrial building. He's said he could get me one, but I've been waiting forever! I've tried searching Ebay without much luck, I have found boxes do this, but many are used for generator backups. While they will work, they are more costly. I really only need the relay, but anything that will work cheap I'd take too! One example is this:

RV Transfer Switch IOTA ITS-50R

I found it on ebay, it is for an RV. The Ebay listing can be found here:

By searching for transfer switch there are a ton of them, but as mentioned many are expensive. Anyone have another option, or a source for these relays cheap? Thanks.
Can you tell me what DC voltage the ham radio runs on? Does the radio automatically adjust for the different voltage?

Most ham equipment is 12 VDC and pretty accomodating to voltage flunctuation. Caviat being that I haven't dealt with some of the high power/high-end equipment i.e. 3KW power amps.