If you can load apps and data with wifi, you might be able to use one of those Virgin Moble phones without paying the monthly plan fee if you do not use it as a phone. If you decide to get the phone instead of GPS, first get the phone. Then see if you can load the apps and data you want with wifi. If you do not have wifi at home, go to McDonalds to access it. If that works, you saved yourself from having to buy a phone plan with a monthly fee of $35 for it.

I use a vintage flip phone that is about 10 years old, my phone plan costs me $80 per year, that is why I still use that as my cell phone instead of the smartphone. (That $80 a year plan is not available to new customers, sorry.) I have a separate smartphone with no phone plan that I can use GPS apps on it but can't use it as a phone. You did not say what your current phone plan costs, but if it is good enough for your needs and costs less than a new plan, do the math.

My above comments should not be considered an endorsement of a smartphone instead of a GPS. I use a GPS, but I carry the smartphone to have as a wifi device for e-mails, surfing web for news, etc. when I stop at a restaurant that has wifi I pull out the smartphone.

Some other phone plan options if you are looking for low cost:
How to Save Money on Phone Plans - US News

The above link did not mention PureTalk, if I got a phone plan for my smartphone, I would get their minimalist plan without data and only use wifi for data.