$500 is just a dart in the middle of the $200-1000 range.
It matters what year it is in the '70s, and then the condition, the condition and the condition.
1973 is usually the worst in terms of workmanship. They couldn't shove them out the door fast enough during the peak of the bike boom. Sometimes the seatstays pop off of the seat cluster! Or a lug will have almost zero braze material in it, just paint! And the chrome on the fork frequently falls off. That said, I like Internationals, and some of them are stunning. Mostly the earliest ones, but some later ones as well. You really have to see and inspect the bike in question. Some, I wouldn't give $200 for. Some, I'd gladly pay $1000 for. They are literally all over the map.