My upgrade was $11 also, which seems way too little.
Unless I'm way underestimating the subscriber base and associated economies of scale, and they really can afford to drive the upgrade rate by making it this cheap, seems like they're leaving a lot of cash on the table. That's actually a touch worrisome, naturally, because it reduces their ability to fund the business through downtimes and make investments into the product (etc). I depend on their product enough that I want their company to be robust and healthy, even if I have to pay more for that to happen. I know they only have a few people to pay today, and I could be wrong about my core assumption, but I don't think they're anywhere near what the market will bear.
I would have paid almost four times as much without thinking myself poorly used. I originally bought sometime in late 2012 and used version 3 since sometime in 2013... which means I've been getting many of the benefits of the upgrade for close to four years. To be honest, I would have even understood if I had been asked to pay the full license fee again and would have done so without pause.
Where do you check? I'm still on the dev build which is one behind the release. I've tried updating in the editor but it states nothing is available. Seems odd that release is 3143 but dev is 3142.
Mine was $0. Honestly thought I'd purchased it before the cutoff date, I can't even remember what I used to use so definitely worth the original price.
Purchased the upgrade license at and incredibly modest price of $30.