I think T-Mobile will be your best bet, even if you can't get the T-Mobile SIM to work in your Inc2. Here's my reasoning...
They have a prepaid "Monthly4G" plan that's $30/month - you get 100 minutes and unlimited text and data, and that's 4G data (well, T-Mobile's version anyway). And it's unlimited, but they throttle after you hit 5gb of data - which you wouldn't, obviously. So that's one good option. Though it would cost you $30/month, and you might not need the data. Though, if you use GPS a lot, you'll want some data - even with map caching, data is required to keep up navigation for any period of time. Anyway, you get the point.
edit: you would likely only get their 4G data speeds with a compatible 4G T-mobile phone... doubt you could get it on the Inc2 through the SIM
If that's still too much, they have one of the better "basic" prepaid plans on the market. A lot of times, the kicker with prepaid minutes is how quickly they expire. With T-Mobile's "Pay as you Go" prepaid plan, you can pay $100 and get 1,000 minutes that
don't expire for an entire year. That's really what makes that deal the best. Text messages count for one minute. Multimedia messages count for two minutes, I believe. There is old school "wap" data, also goes against minutes - but it's almost worthless. So theoretically, you could pay $100 now, and not have to pay $100 again for a year if you didn't use the minutes. That would definitely be a bare bones plan, though, with no data outside of wifi.
I think those would be your best options plan-wise. Virgin isn't bad, but their coverage isn't as good as T-Mobile's. They use Sprint's towers, but without any roaming. Sprint would be worthless without roaming capabilities. Google their respective coverage maps and you'll see what I mean.
Now, the phone. I'm assuming you already own the Inc2. Some quick googling/perusing makes it look like it's not too hard to get a T-Mobile SIM to work in the Inc2, for voice. I'm reading some people having issues with data - but that might not be a concern for you anyway. However, if you can't get it to work, T-Mobile has some very solid mid to top-mid-range Android phones (and some great top-of-the-line phones if you're willing to fork out the cash). You could sell the Inc2 via something like Craigslist or swappa.com, and then turn around and purchase a T-Mobile phone the same way - swappa.com is for buying/selling Android devices... great site.
There's my .02... I haven't exhausted everything, but I've done a LOT of switching around over the past couple of years, and done a lot of digging into getting the most bang for my buck. There might be a better option out there, but I think that'll be a good one regardless.
Sidenote - you can get directions and contact info and lots of other stuff through Bing 411, via text (you text them, they text you what you request). Google 411 used to do this, but they discontinued it. So you can even get a very dumbed down version of "navigation" on a dumbphone.
