You’re probably looking at the “per night” prices and when you go to book you’ve selected more than 1 day, therefore the final price is multiplied by the number of days you’re selected. Also, some site, like hostelworld.com, charges you a booking fee, others like this site and hostelbookers.com do not charge you a booking fee.

Hostels list teaser rates that are probably the lowest off-season rate for the cheapest bed, or 1/3 the rate of the cheapest off-season triple when you have to book all 3 beds. However, some of the teaser rates are so low compared to what you can find on a specific date that I wonder if they’re kind of a scam.

This site has a check list of amenities for each hostel that indicates what’s available and if there’s an extra charge. You may find extra charges for breakfast, Internet or (rarely) linens. The quoted rates in Europe include taxes so you won’t have the surprise of hefty daily taxes like you sometimes have in the US.

I wouldn’t book hostels yet for June, although you can. I usually book 3 to 8 weeks in advance, but if you’re willing to put up with some hassle and settle for second or third choice or a place in the suburbs you don’t have to reserve at all. Just arrive in a city by mid-afternoon and hit tourist information or a hotel booking service in or near the train station. Tell them your price range and that you want a hostel or other cheap lodging. Middle of the road approach is book first night at least a couple of weeks in advance (you don’t want to arrive jet-lagged, sleep-deprived, culture-shocked AND lost and homeless). Book anything involving a special event or where you absolutely have to stay in this hostel on this night as soon as you are sure of the dates. Book last night at least two weeks in advance (to work out airport transportation if you have an early AM flight home). Book everything else from a couple of days to a couple of weeks in advance as you go.

You should talk to site or hostel owner and resolve the issue, rather than presuming something.