I have seen them go for more than $300:
Here are recent NLL.com sales history with 4:
4rh.com sold for $730
4sk.com sold for $910
4qk.com sold for $787
4nu.com sold for $716
4nf.com sold for $555
4nd sold for $760
4eu.com sold for $810
Some high sales with 4:
4rx.com sold for $11,000...