Tablet GPS receivers are accurate enough to give you distance and average speed for the whole ride and for shorter segments (anything over a quarter mile will average out GPS noise). They're not good for elevation, but GPS in general is not good for elevation. The high-end Garmin units include a barometric altimeter to give better elevation accuracy. Fortunately, web sites like Strava will let you upload your GPS track and then automatically compute elevation gain based on detailed topographic databases. Strava will also detect segments you (or other riders) have defined and automatically give you the stats for those. The Strava Android app should run on any Android 4.x tablet. I think it can record without a WiFi connection (and upload once you're back online) but I haven't actually tested it that way.

The only real negatives to what you're suggesting are:

* The quality of $75 tablets is pretty sketchy - they may or may not hold up to the heat and vibration of cycling use.
* They're light on memory so you won't be able to install many large apps (that may not be a problem in your case).
* The screens often leave a lot to be desired an many are completely unreadable in sunlight.
* Battery life on the cheap tablets isn't nearly as good as the high-end models (though 1 - 2 hours on GPS shouldn't be a problem).
* A 7" tablet is a BIG device to have to haul around on the bike. It will fit in a jersey pocket, but the bulk will definitely be noticeable.

Note that having a smartphone does not force you into an expensive phone plan. My wife's Nexus 4 is perfectly happy on a $10/mo pre-paid plan with no 3G/4G data service (WiFi only). You can find a wide variety of lightly used unlocked Android smartphones on Ebay for well under $150. It's a little more of an investment, but most will give you more capability than a low-end tablet and you'll have the convenience of only having to carry one (much more compact) device.