based on the Fact Sheet for this ETF and the recent change in price of GDXJ since march 31, it should now be trading at about .71 times Book Value. If you can believe the fact sheet, PE would be 6.52 (not adjusting for the impact of the change in the gold price on GDXJ earnings.
Using this, I would say the ETF is cheap. not saying it can't get cheaper. Not saying it's a buy.