The price has crept up over the last 4 years. Figure 900-1100 USD, and if it includes the HK-05 quick release scope base, add about 500 to it.
If the stock is all beat up and there's some rust, the basic gun can go for 7-800 USD. Those are my observed GB prices.
The magazines have gone up, too. For new, figure 125-150 USD for the 5-round and 200-275 for the 15-round. Like-new or used, the price is almost the same, they're so hard to find in quantity. Triple K does make some aftermarket 10 and 15 rounders, and those go for $30-50 each.
Aftermarket buffers for s.n. < 15k and > 15k are available, about 40-50 USD each.
PS, I'm looking for a receiver cap for one of my HK-300's, for serial number LARGER than 15,000, if anyone has one.