If you want a really solid solution, It turns out you can buy a 100 or 300A shunt from Mouser. They are in the $45-55 range. Here is the link which will take you to their online store:
You can use these with any standard DMM or analog meter that can measure 50mV. The concern with the previously described solutions is handling the power in the shunt. These shunts are designed for the amperage you're asking to measure. The wire idea is really cool, but calibrating it will be more tricky than you might think at first. Also, it has a tempco of about .4% per degree C. As the wire self-heats, the value will change.
If you prefer an analog meter, they're for sale too, on the same page!
My search on Caswell's page turned up no products for sale or I would have recommended those first. It could be that Ebay might be a source for these...but you might not get what you think you're getting especially if it were abused. My batting average in buying electronic instrumentation on Ebay (and having it work to spec) has been below 50%.