I got mine at the dealership when I was a noob. It was about $25 then I went to the local swap meet and had them embroider a TRD logo in it to match the ones they did for me on my seat covers. Gosh I was a noob then. I coulda spent that money on an air tank or something else. I'm talking about the embriodery not the covers. The covers and dash mat were a good idea. Anywho, I've got one, it was about $30 from the dealer and it fits fine. After time though you'll probably want to buy more velcro. The Vegas heat is having it's toll on the velcro stuck to the dash.
DashMats4Less in suede for my wife's Sequoia are MUCH BETTER than the carpet-like ones she had previously from CoverKing. More professional fit, cut, and finish. http://www.dashmats4less.com/dash_mats.html
BTW, covering XM and GPS wires is a righteous reason.
Nice Garmin. I have a 276c as well, great tool and very accurate. Picked up a 512 card for it and can realy hold some data now. Have remote antenna mounted on very friont left corner of dash and ususally pick up 99% of all available satilites.
FYI: I had initailly thought about mounting mine on dash, but went with a RAM mount off panel below DIN unit and very happy. I was worried about too much background light to interfer with screen contrast. After some experimenting last summer proved to be true and really glad I mounted lower. Also the cops in this area pull you over if your DVD or NAV units sit on dash.