What GPS - a suggestion
I have a Medion car navigation system which uses the Pocket PC operating system (which means it runs a "cut down" version of Microsoft's office products). It’s a MDPNA 100 but I don’t think they are made anymore. There are equivalents for sale from other manufacturers.
OK - what has this to do with aviation.
Well, because it's Pocket PC, you can use a free (but can upgrade for a modest £30 or so) package called Pocket FMS which makes an excellent VFR GPS.
I've used Pocket FMS (and have now paid for the full version) quite a bit and am very happy with it. I fly strictly VFR daytime only in good weather (which you may not do).
Since you need a car navigation system as well, see if you can get one that is also a PDA as well.
I've flown 'planes with a proper aviation GPS and am very impressed with it but somewhat think they are more for the pilot who wants to think they are flying IFR.
Hope this helps you decide.
Roger