This is what you need -
Amazon.com: Garmin 18x PC GPS Navigator Unit: GPS & Navigation
Just like in the picture.
BE very careful as they have a bar unit with pigtail wiring and one with a USB connector, these will not work.
If you shop it on ebay, you should be able to find one for around $35-$40 at tops?
Here is a current ebay listing, $25 or offer with $10 shipping -
Garmin 19N001805 GPS 18x PC GPS Sensor | eBay
A bit better than the $80+ for the Uniden unit.
I have both and the GPS18x does work with the scanners, you will need to have an interface cable for the scanner, not 100% if the 436HP has the same interface as the 396xt and HP1?