Microsoft's Surface 3, released in late March, is one hot product. It could even be a possible iPad killer. With its true x86 processor, it's not much of a stretch to believe that owners of the original Surface RT are drooling over the upgrade, and Microsoft seems to realize that as well.
If you're in that boat, how does a $150 trade-in offer sound? With its lowest-end Surface 3, that'd make an upgrade cost $350 rather than $500. That's actually a very tempting offer.
In order to quality for the full $150, your Surface RT will have to have its original accessories and also be in good shape. Unfortunately, the entire process of the trade-in isn't so straight-forward: you'll need to ship the unit to Microsoft for inspection, and once done, it will email you a promo code to use online. This isn't going to be the speediest of processes, but it could be a worthwhile one.
At the time of writing, the big green button at the URL below which is supposed to bring you to the trade-in site doesn't work; it results in a 403 "forbidden" error. Perhaps Microsoft launched the deal a bit too early? It's hard to say, but it's likely that the site will be functional again later, so keep checking back.