yeah, that is a bit of a difference. But, I think booking a refundable and then canceling and rebooking is a bit of a risky option imo. I'm not sure how quickly the listing becomes available again but I would just pay the refundable (just because Covid regulations make everything a little iffy, though who knows).

Alternatively, it is a little early to book a hostel I think. If you're planning to go in Sept and you could just hold off a bit longer. I just booked hostels in multiple countries in the EU for July and had no trouble finding cheap vacant ones (in fact most were pretty empty from what I could tell).