The $120 pp per night is a great rate. I've paid that before on
DCL, but that was a few years ago and it was a repo cruise from Vancouver to LA. I suppose your perspective on cheap is relative. I found it pretty cheap considering we have a verandah at that price (albeit a white wall).
I looked a little closer at that Marriott by the way. That $340 per night was only two of the nights. I priced a three night stay and the third night was $415. Plus, I had to pay in full for all three nights, with no changes or refunds, at time of booking. In addition, that rate did not include any resort fees or taxes.
I do realize that RCCL would likely be cheaper and I'm certain Carnival would be, but for this trip, we wanted Disney so we are paying the price. We used to live just 15 minutes from
Disneyland so we are having withdrawals here in North Dallas.