The D3200 will definitely hold its value for longer, being that much newer, and with the latest generation technology inside, but that's a good point about availability. You'd need to get it by the end of May at the latest I guess and I'm not sure if that's do-able. I'll make some enquiries.
As for the budget, I was working on your quoted 750 limit, and with the camera at 650 and the 50mm at 100 it does just fit, but if that's too much the kit lens is perfectly fine and it will do you until you can afford the 50mm.