First off, I would highly advise against an individual mobile hotspot device and a long-term hotspot contract
(especially with Sprint and their "4G" network with 3G speeds). Mobile hotspots are just way too expensive, and offer very limited functionality and a very poor battery life.
On the other hand, a Google Nexus 4 phone (requires no contract, goes for 299$ for 8GB, and 349$ for 16GB (more storage for pictures)), and a T-Mobile.com online exclusive 30$/month Monthly4G plan with 5GB of data at 4G speeds, together with the free wifi hotspot (thanks to the unlocked Google Nexus) would be a much better choice to implement your (awesome, might I add!) plan of cutting the cord on your postpaid wireless carrier.
Look at it this way: the price is basically the same as a hotspot service (it's actually cheaper per month; after only a modest initial investment on the unlocked phone), yet you get more data, better coverage (last I checked with their maps and reps, prepaid Sprint and AT&T had no data coverage whatsoever on I-80 in Nevada, i.e. between SLC and Sacramento), plus you even get an extra 100 minutes of extra talk time in case you're travelling and there's no (or limited) data coverage, plus a free (and unmetered!) 911 calling.
An extra benefit of Monthly4G is that you don't actually have to refill it every month right on time (they simply disable your access when you run out, but they still keep your account subscribed to the 5GB@4G@30$ plan for a couple of more months, waiting for your 30$ refill), so, if you're really trying to save, you might even skip a couple of days or weeks from having to activate another 30$ refill card.
And T-Mobile does actually seem to have their own 2G data coverage on I-80 in Nevada. »prepaid-phones.t-mobile.com/prepaid-coverage
Sprint only has roaming on I-80 in Nevada, so, they're definitely
aren't going to give you your 3GB of data over there, that's pretty much guaranteed!
I would strongly advise you to go with the 5GB@4G@30$ T-Mo plan and an unlocked Google Nexus 4 at 349$ (or even 299$), at 299 USD they're basically selling this phone with no profit margin. I got Google Nexus 3 16GB @ 349$ earlier this summer, and although it's clearly not as polished as an iPhone with random bugs here and there, I'm very happy with my deal and how convenient it is to have a fast mobile hotspot ready by your side. Did you know that these Nexus phones have a screen with a resolution higher than MacBooks and ThinkPads? :-) Well, almost — my 13" Aluminium MacBook is 1280x800, my 4.65" Google Nexus 3 is 1280x720. Nexus 4 is 1280x768 @ 4.7". The 349$/299$ price tag for that phone is an Everyday Steal™! By comparison, a 100+$ individual mobile hotspot device with no screen, no phone, no camera, no web-browser, no weather forecast, no SIP client, no Google Voice, no apps, yet same form factor, same battery life, plus more expensive and limited monthly service, plus possibly a long-term contract and activation, termination and overage fees, is not a good deal in my book.