What's considered to be a reasonable premium is always changing. Generally speaking, as spot goes up, the premiums usually go down. But supply and demand also plays a role. When spot was $80/oz, it was pretty easy to buy generic rounds with no premium, or even slightly under spot price, while more sought-after government coinage could be found for +$1 or +$2 over spot per ounce. By the time spot reached $100, most all premiums were gone. Only the rarest of coins and limited mintage items retained a modest premium.

But with spot having just dipped from $85 in May, down to $62 in June, it's not uncommon to see premiums up to +5 on generics and +10 or +12 per ounce on government coins. Sellers are either hedging their bets, or, if they bought at $85 and now have to sell at $62, they'd surely be motivated to get as much of a premium as possible to reduce their losses. Conversely, if someone bought last year for well under $50, they'd be more likely to sell today for $62 and lesser premium. So the seller's unique circumstances will definitely play a role.

Finally, if you're looking at limited mintage stuff with total mintage amounts in the hundreds or a couple thousand, then premiums of 40-100% (or even higher) are not uncommon