My vote is for the 5D classic. There's absolutely nothing wrong with its image quality, and 12MP from FF in real terms is plenty of resolution. It's all Nikon offered until the D800. As Neuro said, 100k shutter life, so it should do you well.
As the 5D classic didn't have a built in sensor cleaner, a used one might need it cleaning. It won't cost much to get a cleaning kit should that be the case.
I don't think there are any other options - the 5D mk II is out of your budget, and if the extra resolution isn't needed, the other tweaks won't help you get better images. And all FF 1 series with the sort of ISO you want will be too much too.