Hotel booking sites with a calendar view, similar to flight search engines?

Not sure if this is what you would be looking for exactly but I did find on Googles hotel search that you can put in a start date and end date and search. When on the search results page you can click on the little bar chart on the right hand side of the dates and give you a little chart of when it's the cheapest. Google flights is similar as well.

This is only a partial answer, taken from my answer to another question. In particular it is only practical for a limited number of hotels, limited number of days and not always precise.

Hostelworld has a price breakdown that we can use with a few drawbacks.

If you can find the hotel/hostel/spot under the bridge that you want to go to on the website, you can specify a travel period ("stay") of up to 15 days. Then pick your place and go to where the price is displayed. You will find the option "View price breakdown" give you the price per night:

I took the freedom to fast-forward to 2016 when school holidays start Saturday 24 September. Hostelworld has one property for Dubbo, an Ibis. I honestly don't see an effect due to the school holidays there, prices go somewhat up the Tuesday before.
I double-checked with the hotel website on three of those days and interestingly I always get the same price displayed, i.e. the above method may not always be useful.

And here are some more catches:

1. You have to find the place you are looking for on the site. Hostelworld does have a decent selection of hotels, but you will not find a Grand Hyatt, apologies.
2. If you are looking at prices over long periods, you have to do a ton of searches due to the max 15 days stay limit.
3. Your desired hotel/room type may not be available on one of the days in the 15 days and not be displayed.
4. Some hotels may have a shorter maximum stay and not enter that list (even though I found them displayed).
5. A different rate may apply for your actual duration of stay than for the 15 days search period and the hotel might have a minimum duration of stay.