Delete cookies or just use another computer. Some sites track cookies. Its not trying to jack up prices to get more out of you. Its trying to create urgency. It was $100 earlier. Now $120. What if I leave it til tomorrow? $150? I better book NOW. Airfares use same method. Some will track IP address but more likely cookies.
In your case it could be neither since you also changed dates. Might be 4 rooms available at $129 and anothe 4 at $159, etc. The dates you chose are booked out in one price level. Im not saying the room type is different. Same room. Just different deal.
Try a different aggregator site. Hotels.com.au , agoda, hotelscombined, etc.
