Can I just buy a GPS system and use it as is or do I need to subscribe to a monthly service or something? In other words is a GPS a one time thing you buy and use or do I need the service also for it to work.

With a GPS system you do not need to subscribe to a service. It works by receiving signals from satellite. I have a Garmin GPS that I have had for about 2 years and love it!  It's an older model because I got it from Ebay but all I have to do is plug it into my car charger or use batteries, put into the GPS the destination I am going, mount it to my window and wait for it to signal in and bring up the map. 

Also most all GPS systems provide you voice directions or you can turn it off and just keep an eye on the map directions.  It is great to have cause I don't know how many times I would have been lost without it.  Only downside is that the map CD that you get with your GPS usually has to be updated at some time or another depending on what system you get.  For instance, I was able to receive a free 2009 map update but to unlock the map I would need to pay $75 to have an unlock code :(.  If you buy one brand new you shouldn't have that problem though. I still use mine and like I said I couldn't go out of town without it :).

All you have to do is buy the unit itself. Some GPS do have extra features like weather and traffic allerts and map upgrades that may require additional one time costs or monthly costs. I have had Garmin, Tom Tom, Navigon and Magellan and i love my navigon. It works great and tells you when you are going over the speed limit which has saved me many tickets. Mine also came with free traffic and weather updates as well as detours and street name announcing. I get great reception everywhere i go and can find many points of interests. I purchased mine from dell for under $125

I got my husband a TomTom due to his work, got it at Wal-mart, all I paid for was the unit itsefl.  He has to go on alot of country roads and it has worked just great.