That's an expensive resistor. However four 12V automotive headlamps wired in series could be a fairly cheap load that should draw about 200W. Double that up with another string in parallel with the first and it should draw about 400W. Headlamps are pretty inexpensive.
I can get two 24V/250watt overhead projector bulbs for $4 on amazon. If these specs expect an AC source, could I expect the DC resistance here to be too much different than the AC impedance at 60hz?
I doubt it. I'd try them. O/H projector bulbs get very, very, very hot and are almost always forced-air cooled by a fan to keep them from destroying themselves. Watch out.