If I were searching for a steam crane, like the unit on the ebay listing, and found one at a train show/swap meet, I’d likely be willing to pay $10-$15 for it. Although crudely detailed (such as the molded on ladders), units like this can be fun to detail and spruce up. Imho, $15 seems reasonable which would be “my best offer”. Of course, the seller may feel differently, which is his right.
Some of you probably remember my thread regarding this diesel crane from 2 years ago:
I won it on ebay for $14. With shipping it came out to $17.50.
Although a crude AHM model, the railroad I primarily model (SCL) had cranes that are strikingly close in appearance to the AHM unit.
Here is the thread: