sounds pricey, There is a LFS near me that has had a 30 inch aro for sale for almost 7 months, it had DE, but other then that a nice fish. Originally they wanted $200, but now its $125...
if it was a juvenile arowana the barbels would grow back, no prob. but in this case where it's a full grown it won't be easy to grow back. it takes longer for an adult to grow back its' barbels compared to a juvenile.
I'd offer the guy $150 for one of the smaller two. They'll be nothing but a money sink to a LFS, if they feed them at all. If he says no, just wait a while. After a month of having 3 giant silvers still for sale he'll change his tune. Big fish are harder to move than little fish. Low demand = low cost. More so since silvers are a dime a dozen.