Lets say I pick up a Garmin 276c. I see it comes with a marine mount. Will i need to buy a card? $109-169, Ouch? Would I need to also order a cigerette plug? Will I need to order maps? Are the maps free? Will the marine mount work well on an 06 Crossfire 700? What maps work best in all of Michigan?

I purchased the auto navigation kit for my 276c. https://buy.garmin.com/shop/shop.do?pID=1075
This kit covers all my needs for snowmobile and car.
You will need a card to hold any additional maps ie snowmobile map.
you can operate off of the battery but if you want to power it from your snowmobile you will need a power cord.
There are snowmobile maps available for free on this site. Member RWS has generously made them available. Garmins maps are not free.
I have seen photos of the marine mount on snowmobiles on this site so it does work.

I would not travel without mine.

I have snowmobile trail maps on my site you can download for free. There are instructions on the site for installing them without Mapsource (which you won't have if you don't buy any Garmin maps - though you can get it free from Garmin.com by downloading and installing their training center software followed by the Mapsource update).

You will need a card to store the maps. One drawback of the 276c is that you have to use Garmin's pricey cards rather than a standard inexpensive microSD cards.

Out of the box, the GPS has almost no maps at all, so if you want to use it for the car, you'll need City Navigator. For outdoor use, you would want Topo 2008, though my maps have roads, lakes, and rivers so it's not essential to have the topo map for snowmobile use.

Check out RAM mounts for a variety of mounting options.

i like this one i use it most of the time over the garmin topo http://www.vvmapping.com/