It's perfectly simple to make your own, if your stuck, but not much cheaper - but you can make it do exactly what you want.
You only need the most rudimentary soldering ability.
I've done it successfully in three different vehicles, in each case, the requirement was different. If you send me a personal message with your requirement and a fax number, I'll be happy to draw one up. But try the proprietary one first.
_________________________
Politics and Ideology: Not my bag