I have a Nuvi 500 that came with the 100k maps and purchased the 24k CD (more coverage). The maps off the CD are somewhat better, but I don't think they wre worth the expense and the software is not very user friendly. There is a place in Vegas called GPS city. They are fairly new but have good prices and you might be able to look at the maps prior to purchase.
The Montana is a sweet unit. I thought about getting one. Has some nice features that the Nuvi 500 doesn't have. Just couldn't swing the price though. If you are looking for one just for the jeep, the 500 has the 100k maps and the street maps. If you are looking for something to go hiking with, I would look at other units. You might try looking at the Oregon 500.
I have the Garmin 1350 and have the 24K maps. Works perfectly, but they haven't released an update since 2009. I contacted them a week ago and was told they have no announced release date for an update. I can burn a copy to DVD if you want it. Save yourself $100.
Sounds like the 100k would be better, but it's not. The 24k has way more detail.
I tried to reply to your PM, but your box is full. Here was my reply:
You don't even need to use the SD card. You would need the latest copy of Garmin's MapSource. I could burn that onto the DVD too. Everything can be read and uploaded to your GPS from your computer.
I wouldn't be able to get it to you today. I'm not feeling very well and my wife stole my Jeep. I'll go ahead and get the DVD ready and I should be able to meet up with you somewhere over the next couple of days.
I'll be sure to add the newest copy of Mapsource to the DVD.
In the meantime, have a look here: http://www.gpsfiledepot.com/maps/state/nv
It has a few free GPS maps you can use with your Garmin. I have three maps installed on mine. When offroad, I use them as overlays. If a feature isn't showing up on one map, it's likely on one of the others.